What type of planetary-mass object would Planet Nine be?

It is a planet - either a gas giant core, a mini-Neptune, or a super-Earth.

First off, Mike Brown has stated outright

“It is a planet—there’s virtually no doubt,” he said. “What we now call planets are objects that can gravitationally dominate their neighborhood. Pluto is a slave to the gravitational influence of Neptune. By area, Planet Nine dominates more of the solar system than any other known planet—it’s only because of this that we can infer its existence. And because of this we’re pretty sure it’s not a small object: it’s at least ten times more massive than Earth and five thousand times more massive than Pluto. In many ways, you could argue that this is more of a planet than anything else in the solar system.”

I wrote an answer to How was the hypothetical ninth planet kicked so far out of the Solar System? that discussed the possibility that the ninth planet is the hypothetical 5th gas giant proposed by Nesvorný (2011). The details can be found in that answer, but basically, Brown & Batygin's reference to previous papers by Morbidelli et al. suggest that they think that this is what remains of an ice giant, like Uranus and Neptune, that formed near Saturn and Jupiter but was ejected in a series of gravitational interactions that led it to the Kuiper Belt and beyond.

That said, Batygin's estimates place the ejection of this planet way before previous models of a 5th gas giant predict, so either we accept models with a 6th gas giant (also an ice giant) and say that both of these were ejected independently of one another - not impossible - or we go for some other option. The bottom line is that this is a planet, if we go with the above assumptions.

Two other guesses have been made based on the planet's mass, estimated by Brown & Batygin at about 10 Earth masses. One is that it is a very massive super-Earth, hanging around the proposed upper mass limit for those objects. This implies that the planet is rocky, but does not imply anything else. The other guess is that it is a mini-Neptune, with a predominantly gaseous composition but at about the same mass. The super-Earth hypothesis arose in part because of claims a long time ago about the ejection of a 5th terrestrial planet.

I've used the term "planet" throughout this entire answer, and that's because this object may be one - and most likely was in the past. Let's look at the IAU's three major criteria to be a planet:

• It orbits the Sun. This is definitely true, if it exists. Also note that if this is a captured rogue planet, as some have proposed, then we can still call it a "planet", because it now orbits the Sun.


• It is in hydrostatic equilibrium. This is most likely true, and is true if any of the three models I suggested above are correct.


• It clears its neighborhood. This is a bit iffy. It clearly influences objects around it, but we don't know much about those influences besides observations of the six Trans-Neptunian Objects (TNOs) Batygin & Brown studied. That said, an object with a mass of 10 Earth masses will most likely clear the neighborhood around its orbit if it has a stable orbit, which should be the case here. See the quote at the start of this answer for more information.

radiation - What is the modern state of the theory of evolution?

My friend Brightblades is right in one thing. It seems your teacher was working off a caricature of what the theory of evolution actually says. First of all, you should read Sklivvz's excellent answer at this question. Now to address the elephant in the room, the accident at Chernobyl only happened in 1986. That was only 26 years ago. In that timeframe, noticeable effects in an animal population really would not be at all noticeable. Furthermore, the paper cited by Marta Cz-C actually shows that there have been some changes (in fungi though, not animals).

fungi seem to interact with the ionizing radiation differently from other Earth’s inhabitants. Recent data show that melanized fungal species like those from Chernobyl’s reactor respond to ionizing radiation with enhanced growth. Fungi colonize space stations and adapt morphologically to extreme conditions. Radiation exposure causes upregulation of many key genes, and an inducible microhomology-mediated recombination pathway could be a potential mechanism of adaptive evolution in eukaryotes.

Read the rest of the paper for more information on how there have been some other slight changes to fungi at Chernobyl as well as other locations throughout the world.

Now I am going to repeat a bunch of stuff from one of my web pages that talks about evolution. This web page is set up mostly to deal with creationist arguments, however, the caricature is so severe as to warrant this. As I said earlier, evolution is a population phenomenon.

Evolution acts upon heritable variation of characteristics, and you can only have variation of this sort within a population. A single individual organism, at least if its a multicellular eukaryote, has a fixed genome. It can't change what it has inherited. But a large number of organisms can all have different genomes, and can disseminate variation via inheritance to the next generation. It is upon the population as a whole that evolution acts, with various mechanisms coming into play to remove some variations from the population, and propel other variations to numerical dominance within the population. The organisms in question remain part of that population, and within a generation, those organisms don't change. But the moment a new generation is produced, dissemination of variation can result in the appearance of a new feature in one or more members of that population. If that new feature leads to greater reproductive success for the organism possessing it, that feature spreads through the population, as more and more future offspring inherit it. Over time, the population changes, and more and more organisms with new features appear within that population.

Understanding inheritance basics and mechanisms for changes (genes), we have all that is needed for the appearance of cladogenesis events. Split a decent sized population of living organisms into two, and let's call these new, separate populations A and B. Now let a barrier be erected between population A and population B, so that individuals from one cannot reproduce with individuals from the other. This barrier can be an insurmountable physical obstacle, for example, but this need not be the only form such a barrier can take. Now, first of all, there is no reason whatsoever to think that population A and population B will start off in identical states to begin with. After all, those two populations were derived from an original population comprising lots of organisms with different genomes, and the likelihood of population A and population B being identical at the start of this process is vanishingly small. Then, once our barrier is erected, and our populations are allowed to reproduce separately from that point on, there is no reason to think that those populations will move in the same direction in the long term. Indeed, it is far more likely that they will be subject to different environmental and ecosystem influences, and those different environmental and ecosystem influences will shape the long term heredity of those populations. Indeed, that's all that natural selection IS - it's a single, concise term used to encapsulate all of those environmental and ecosystem influences succinctly, and additionally to encapsulate the fact that those influences affect the inheritance of characteristics within a population over the long term.

As a consequence, any two separated populations of living organisms, that originated from a single population, will diverge from each other. If the extant influences on those two populations are sufficiently different, that divergence will take place more rapidly. Eventually, we will arrive at a point where those two populations become sufficiently diverged from each other that individuals from population A can no longer produce viable offspring with individuals from population B, and vice versa. When this happens, we have a speciation event. Indeed, this has been observed taking place in the wild AND in the laboratory, and has been documented in the relevant scientific papers. So, if anyone wishes to assert that there are 'magic barriers' to speciation or other cladogenesis events, then reality doesn't agree.

You will not have any animals giving birth to any radically different animals as a result of radiation. Most changed sue to radiation will not provide any particular advantage to an animal anyway. Also, a change may also be dependent on a previous change and require many generations to fully manifest. All this was demonstrated by the long term evolution experiment led by Richard Lenski at Michigan State University.

So in essence, your teacher was just plain wrong. As for the findings of the past 20 years, we are always learning more and more. For instance, there has been an explosive capability in DNA analysis and sequencing, which has only provided more support for the theory of evolution. A mechanism that Charles Darwin could not have had any idea about in his day and age, yet it perfectly supports his conclusions. Again, read the answer provided at Skeptics.

human biology - Is there a relationship between efficiency of cellular metabolism and warm-blooded-ness?

While heat is lost during glycolysis, a lot more heat can be lost during chemiosmosis. This is the movement of H+ (protons) across the inner mitochondrial membrane. The energy potential of having a greater concentration of H+ on one side of the membrane usually powers ATP synthesis through ATP synthase. In mammals, however, special proteins called uncoupling proteins (UCPs) can make the membrane 'leaky' to H+, so the energy is lost as heat, instead of being used to make ATP. This is called non-shivering thermogenesis, and usually happens in brown adipose tissue (because fatty acids are used to enable UCP production).

It is not that glycolysis in ectotherms is less efficient (as far as I'm aware), but that ectotherms have different levels of different types of UCPs. Some UCP genes may have their expression altered in response to colder conditions (e.g. UCP2 and 3 may be upregulated) or the genes may not be present at all (e.g. UCP1 is not present in birds and crocodiles).

A better summary of UCPs in reptiles etc. can be found in this abstract:

http://rspb.royalsocietypublishing.org/content/275/1637/979.long

Genetic effects on personality - Biology

The problem you are looking for is called the "Nature vs nurture" debate. Lots of scientists have written lots of books and papers and done lots of studies on the subject. As you can see, the title of the debate already includes the two main concerning factors: nature (genes) and nurture (environment).

These of course each include a variety of ways in which they influence personality. Genes provide the biological basis for your personality, they determine how everything in your body works¹. At the same time, these genes build a system that has a life of its own - your brain.

It consists of neurons, and nobody knows how personalitites comes about from them exactly but somehow they do. Neurons reshape all the time in ways that no other cells do. The connections between them, synapses, are formed, destroyed, reinforced or weakened all the time - in response to things that take effect on them, for example the things that you see and hear, smell, taste and feel. A very interesting subject in this field is the study of neuronal networks, giving some insight into how memory and learning may work.

But while this may seem like external factors must then be more important for personality, it depends on the setup provided by your genes how your neurons respond to certain influences - what concentrations of neurotransmitters they produce and secrete etc.

As you can see, the only thing that is really safe to say is that it is not "either or", both definitely play a role.

¹But even the biological development of the body has non-genetic influences - at the moment I can think of epigenetic inheritance though this seems to be disputed (see comments). Apart from that as far as I know there are uterine influences on embryonic development. And then there are the more or less obvious external influences such as cutting things off before they develop.

Do massive OB stars accrete mass the same way as the black holes they turn into do?

Many, if not all, stars will, in their birth phase, have an accretion disk, or circumstellar disk, around them, formed of the material from which the star forms. This disk dissipates in a few million years, both due to the material accreting onto the star, due to material being blown away by radiation pressure, possibly assisted by dust grains, and due to depletion of the material to rocks and planets. Friction in the disk causes it to heat up and be observable in the infrared. After this phase, the star usually won't have an accretion disk. That is, until they die.

As you suggest, a star that later on goes supernova can accrete matter from its "reverse shock", i.e. matter that is falling back due to the shockwave hitting the surrounding interstellar medium. More often, though (I think), will the accretion disk be made of material from a companion star: If one star of a binary system turns into a black hole, and then the other star starts to evolve into a red giant, threspassing the Roche limit, it will transfer matter to the black hole.

As you say, the black hole's mass isn't stronger than the original star's mass, and thus the gravity at a given distance is also not stronger (in fact it's smaller, since it has blown out most of its mass in the explosion). However, due to its much smaller size, the accreting matter can come much closer before being sucked in. Coming much closer means being in a much steeper gravitational potential and reaching much higher speeds, i.e. being heated to much higher temperatures. Hence, black hole accretion disks can be detected in X-rays

human biology - Why apes started to contemplate and become altruistic?

I think this is a difficult question all around, which is why its a little uncomfortable for some to be entertaining questions which are often seemingly metaphysical in nature.

I think also that it is true that biology and neuroscience will have a big impact on the question, its also fair to say that the jury is still out on this question.

The genetic anthropologist Svante Paabo is one of the most engaging researchers in this question. He started out studying the difference between the human gene sequences and the chimpanzee to try to suss out the specific genes which might be be responsible for out social selves. So from this point of view, it might be that intelligence started at most about the time of human chimp divergence, 8-25 million years ago.

Finding the specific genetic structures that convey our unique cognitive or social abilities would certainly pinpoint that time much more accurately. There is just 1-4% difference between the chimp and human genome sequences (depending on how you calculate it), but even 1% of a 5 Gb genome is a lot of differences and no intelligent mutant chimp has been found (that they've told us about!) .

Since then, a lot of interest has focused on assembling a complete Neanderthal genome sequence. Since Neanderthals diverged from humans about 500k years ago, and there's plenty of evidence that they were intelligent, comparing the three genomes (human chimp and neanderthal) would help pinpoint the specific genetic elements which are distinctly human.

If it is a mutation or set of mutations as the current thinking implies, there is a good chance that it is a combination of strong selection and accident. Its true that cooperation is often enjoys a strong selective advantage, but it doesn't make you smart or hospitable. When we talk in biology we don't say altruism, we say cooperation. If such cooperation happened only because of selection, we would see such behavior in other primates. So if we see this, I would lay odds to look for a rather complicated story...

Another interesting person to read is anthropologist Terrence Deacon, who is trying to understanding the terms with which we define intelligence. About ten years ago there were actually experiments that showed that chimpanzee some strong candidate intelligence genes related to cognition could be put into people (who needed gene therapy because they had lost cognitive function) and restore that function. Apologies, this is anecdotal - i saw him give a great talk, but he's moved on a bit and can't find the references.

This is important I think because the fundamental definitions of human intelligence have failed over the years, from the old chestnut of using tools, to a recognition of mortality, to awareness, animals have surprised us, particularly primates. I wonder whether we will be able to confirm these vital factors until we get a monkey asking for the keys to the car so that they can go get some pizza.

rest - Does aerobic exercise training change resting metabolism?

In order to answer your question, it's best to review how the body's energy systems work. An article called "Death by Prowler" by Matt Reynolds has a good overview. It's an educational read, but I'll summarize a couple high points here:

• Aerobic activity burns more fat in proportion to sugars.


• Aerobic metabolism does not shut off when you push into higher demand energy systems (i.e. anaerobic activity).

Based on the Katch McCardle algorithm, resting metabolic rate is most affected by the lean mass you have. I.e. more lean mass, more calories burned at rest.

Now, the bottom line is this: you will burn more calories per given amount of time when you exercise at an anaerobic level. The major caveat is that you won't be able to keep up the anaerobic exercise as long as you can aerobic exercise. Even though the majority of the calories burned during exercise will come from blood sugars/glycogen in an anaerobic state, the body will have to free energy from your fat stores to make up the energy demands. This is what is commonly referred to as the "after burn" effect.

With aerobic exercise, your body is able to keep supplying energy at the rate it uses it. While this is sustainable, once you stop exercising, you no longer have any demand for more energy. Thus, there is no increase in resting metabolic rates.

human biology - How many genes do we share with our mother?

Say x is the percentage of an allele in your mom (or cousin, or brother). Say c is the filial similarity (brother=.5, son=.5, cousins=.125, etc.) of the allele. Say y is the general probability of having that allele in that population (assuming mom is the same species with you). Say f(x,y) is the expected value of the number of allele that you have.

Then f(x,y)= c * x+ (1-c) *y

In other word. There is no contradiction in the idea that we are 98% similar with monkeys and yet only 50% similar with our own mom.

Here, the world similar is used in totally different sense.

f(x,y) is 99% for most allele. Now let gy(x)=f(x,y) then

gy'(x) is c.

In other word, for every allele your mom have, it'll improve the expected value of you having the same allele by half. For each allele your cousin has, it'll improve the expected value of you having the same allele by 1/8th. That is for the same y. For most y, similarity is 100% nevertheless.

Say Ann, Beth, and Cindy has AA, Aa, and aa alleles.

Then Ann's sons have 25% higher expected value of having A alleles than Beth, and Beth have 25% higher expected value of having A alleles than Cindy. I say nothing of actual probability distribution.

Ann's cousins have .0625% higher expected value of A occurrence than Beth's cousins and .125% expected value of A occurrence than Cindy's cousins

Disclaimer: We do not take into account that people mate with those who are genetically similar but not too similar (i.e. no inbreeding).

Another way to see this is to look at y. For rare genes y is small. Hence.

50-50 is for genes that are rare and family specific. If your mother is color blind (100% carrier), the expected value of the number of color blind carrier is improved by 50%. It doesn't mean you'll be color blind. We'll have to go to the technicality of dominant vs recessive. But that's the idea.

For genes that are NOT rare, say genes that make you have 2 feet and 2 hand, you still share all your mom's genes. That's because everybody have that. Your mom have that, and your dad have that, and so is everyone else, including chimps.

Is this what most directly answer your question?

Again the issue is rarity. For rare genes P(You have it|mom have it) is 50%.

For common genes,

P(You have it|mom have it) = P(You have it and mom have it)/P(mom have it). //By bayesian rule

That is 1/1, which is true.

It's just obvious, probability = 1, that everybody has it.

Source: selfish gene by Richard Dawkins
I am a mathematician. Now prove me wrong.

positional astronomy - What is the Northernmost Latitude of Saturn?

To add to the other answers, if you were in a place where Saturn could be directly above, make sure you get there just over an hour and a half early.

Now; do you need to be there when Saturn is directly overhead or when the light from Saturn is directly overhead?

The closest Saturn gets to earth is approximately 1,200,000,000 km (750,000,000 miles), light takes 1 second to travel 300,000 km therefore the light from Saturn would take a minimum of 4000 light seconds (1,200,000,000 / 300,000 = 4000) 4000 seconds = 1.11 hours. So you are seeing Saturn where it was just over an hour before. This could increase to over 1 1/2 hours depending on the distance between Earth and Saturn at the time (max approx 1,700,000,000 km).

human biology - Why does looking at bright light trigger sneezing in some people?

You are talking about the photic sneeze reflex.

The mechanisms are not entirely understood, but it affects 18-35% of the population.

According to Wikipedia (although this passage is not sourced):

The probable cause is a congenital
malfunction in nerve signals in the
trigeminal nerve nuclei. The fifth
cranial nerve, called the trigeminal
nerve, is apparently responsible for
sneezes. Research suggests that some
people have an association between
this nerve and the nerve that
transmits visual impulses to the
brain. Overstimulation of the optic
nerve triggers the trigeminal nerve,
and this causes the photic sneeze
reflex.

And, it could be advantageous:

On the other hand, some people with
the trait feel that it is
advantageous. In the event that nasal
discomfort occurs, but to an extent
that is insufficient to induce a
sneeze, intentionally seeking and
finding a light source facilitates the
sneezing process and is in turn a mode
of relief.

Also, anecdotally, as I too photosneeze, I can see an advantage: should the atmosphere become weaker in the future, and allow more light to enter than we are accustomed to, it would discourage looking directly at the sun.

gravity - Will gravitational waves too far away ever reach us?

Gravity is the curvature of spacetime, and its effects travel at lightspeed. However, space is expanding; eventually, light from distant galaxies will become more and more redshifted, and we will no longer be able to see them (source).

As such, there is a limit to how far we could ever possibly see, since light too far will never reach us due to the rapid expansion of space...or at least, if I'm understanding this correctly.

Now, gravitational waves travel at lightspeed. So, after enough time, when an object's light no longer reaches us, will its gravity no longer affect us either?

A better rephrasing is: at a certain point in time, will the gravity of any extremely distant object — even the most massive stars, black holes, or galaxies — simply not affect us whatsoever, in the slightest?

black hole - What are the dimensions of LIGO Detector evacuated chambers?

The arms are $4,mathrm{km},times, 1.2,mathrm{m}$:

From the LIGO webpage:

The 1.2 m diameter beam tubes were created in 19-20 m-long segments, rolled into a tube with a continuous spiral weld. While a mathematically perfect cylinder will not collapse under pressure, any small imperfection in a real tube would allow it to buckle (a crushed vacuum tube would be catastrophic). To prevent collapse, LIGO's tubes are supported with stiffener rings that provide a significant layer of resistance to buckling under the extreme pressure of the atmosphere. The tubes must withstand these stresses for at least 20 years.

human biology - Energy use by muscles, actual work done by muscles and more

1) It depends on each country and your minister. In Finland, the thing is done so that it says the energy stored in food, which will be released if burned.

2) It is the energy pushed to the bike when the bike does not take into account your pulse. If the bike is smart one, it takes into account your pulse rate, then it tries to estimate the amount of energy released by your body. This is done differently among different manufacturers of those watches.

3) By the way heart is a bunch of muscles, a myogenic muscular organ! So consider instead heart and some part of lungs. Very broad problem otherwise.

red giant - How can white dwarf form Oxygen ? (Temperature problem)

I’ve got a question about white dwarfs and oxygen.

I read in a book that a temperature of 100 million degrees is required to fuse Helium in the core of a red giant. The Helium fuses into Carbon by the triple-alpha process.

It’s also written that, after a temperature of 350 million degrees is reached, the core of a red giant ceases to be degenerate. So, the core is able to expand and its temperature is controlled. The core won't reach a temperature of more than 350 million.

But my teacher has said that a temperature of 600 million degrees is needed to form Oxygen from Carbon: Carbon fuses into Neon and by photodisintegration gives Oxygen.

So, how can there be Oxygen in white dwarfs, if we don't reach a temperature higher than 350 million degrees? By what process can oxygen be formed in a red giant?

Mitosis in human body - Biology

In many cases cell division depends on the stage of development an organism is in. The rate of cell division is obviously much faster in a developing organism and from what I understand fully differentiated cells such as neuron and those in skeletal muscles don't divide (correct me if I'm wrong here).

In early development totipotent cells (stem cells that can become anything) begin to differentiate dependent on environmental factors, turning into multipotent (partially differentiated) cells that can only lead to certain cell types. For example: mesodermal precursors can differentiate to myoblasts, which can go on to differentiate into myotubes, later forming muscles.

Epithelial and and blood cells are the two of the main types of cells that need to be constantly replaced in developed organisms. As far as I know cells lining the gut epithelium are fastest to divide. They are created from stem cells in 'crypts' (pockets) in the lining and are pushed outwards, where they are later broken down (by what I would assume would be abrasion and intestinal juices). My book gives them a lifespan of 3-5 days. External skin cells are much slower to divide (though I'n not sure by exactly how much).

Red blood cells have have a lifespan of approximately 120 days. They are replenished by stem cells in the marrow of certain bones (e.g. a femur). Neutrophils are the next most common blood cell, with a circulating life of 8 hours (but lifespan may be a few days). Per day, roughly equal numbers of RBCs and neutrophils are created and are most numerous new cells created per day. Lymphocytes, another white blood cell, are responsible for immune 'memory' can persist for years. The fastest recorded mitotic cycle for a mammalian cell (in culture) is ~8-10hrs.

Likelihood of extra planets in systems identified by Kepler?

There are many planets that Kepler couldn't detect because the ecliptic is inclined so no transit occurs from the perspective of Earth. We are much more likely to see a transit if the transiting planet is close to the star, and so in Kepler's sample of stars, a disproportionate number of the planets discovered orbit very close to the star. It is probable that most stars have planets, and many of those planets orbit much further out than the average in the Kepler sample. And, moreover, the stars which have been found to have planets are likely to have others, orbiting further from the sun, and inclined, so they are not detectable by transits. Kepler has not detected Earth size planets orbiting in the habitable zone of sun-like stars.

So far we do not have the technology to detect a planetary system that mirrors the Solar System. Our alien friends, if they are very close to the ecliptic may detect transits of Earth but would likely miss the other planets. And there is no reason to suspect that the Solar system is not typical in the range of inclination of its planets.

taxonomy - Could someone recommend a book for surveying species?

Judging from your response to Gurav in the comments, it sounds like introductory zoology and plant biology texts would fit the bill.

For zoology, we teach from Hickman et al's Integrated Principles of Zoology. It outlines the major phyla, their defining characteristics, with plenty of specific examples scattered throughout. There are nice little problem sets throughout, and it goes into a solid amount of detail for a first or second year zoology course.

For plants, I've used Graham et al's Plant Biology, which takes a similar general approach. Though it's perhaps a bit broader, and less species-focused.

Both of these books outline the major relevant groups, and use 'representative' species to illustrate various biological points throughout. They might be a good place to start!

molecular biology - Why do we add salt when precipitating DNA?

The role of the salt is to neutralize the charge of the DNA's sugar phosphate backbone. This makes the DNA less hydrophilic (less soluble in water).

Ethanol has a lower dielectric constant than water so it's used to promote ionic bonds between the Na⁺ (from the salt) and the PO₃^- (from the DNA backbone) causing the DNA to precipitate.

communication - Were the Voyager Golden Record / Arecibo message tested for decodability

I was wondering if the microgroove golden records they put on the Voyager spacecraft, or the Arecibo message, along with instruction on how to decode it, were first put to the test with the subjects most likely to decode them, i.e. humans.

I would suppose they were, as Carl Sagan, who was part of the team who designed the messages, takes the complementary stance in Contact to have humans decode an alien message, but incidentally the alien message mentioned looks quite too close, both in methodology and content, to what humans sent a decade earlier, non-fictionally, on the Voyagers.

So, did they test whether or not if these messages are decodable, and was a 100% interpretation achieved?

Could dark matter assist with star formation?

Strange you should ask - I am currently working on a paper on NGC 2516 - "the southern Pleiades" and looking at the dynamical status of the stars compared with the distribution of visible mass.

Our conclusion is that the radial velocities of the stars are in virial equilibrium, with velocity dispersions that are entirely consistent with the mass that is present in the stars that are visible. So, no need for dark matter there - you could probably rule out any contribution of more than about 50% of the visible stars. (NB the point of the work is not to look for dark matter, is is not expected - see below).

This is one of the first very detailed measurement for an open cluster (like the Pleiades), because the velocity precisions required have to be considerably better than the velocity dispersion. And for a sparse cluster like the Pleiades, this is $<1$ km/s, which is challenging.

There is one old paper by Jones (1970) that uses proper motions in the Pleiades to estimate a dynamical mass based on virial equilibrium of $690 M_{odot}$, which compares with $470 M_{odot}$ from directly counting stars. But Jones points out that the latter number is a lower limit (they certainly couldn't see very low mass stars and brown dwarfs in their study) and the former number has large uncertainties. So there is no real evidence for any "dark matter".

The dynamics of globular clusters are easier to measure - they are more massive and have much higher velocity dispersions. The general picture is reasonable agreement between velocity dispersions and inferred mass distributions from counting the visible stars. There are of course uncertainties, but there can be no large dark matter component. Limits as small as $<6$% dark matter have been set in some clusters (e.g. Ibata et al. 2012).

The first Gaia satellite results, due in about 18 months time, will blow this field apart. We will have exquisitely precise tangential velocities for $sim 1000$ stars in the Pleiades.

Dark matter is not expected to play a role in small scale (star cluster) formation. When clusters form, the dissipation of energy in gas interactions is what allows them to end up as bound systems. Dark matter is dissipationless. As the escape velocity of these clusters is 1-10 km/s, compared to velocities of hundreds of km/s for datk matter, there is not even expected to be any gravitational concentration of dark matter. This is quite different from galaxy formation, which is associated with pre-existing dark matter structures.

neuroscience - Can one dendrite pass through another?

I can't think of any reason that would explicitly prohibit a dendrite from travelling through a space created by another dendrite's branching pattern. In non-EM images of dendritic branching patterns I don't think I have ever observed dendritic loops, but of course, that has nothing to do with whether or not they occur. Nonetheless, I think there are more likely explanations for what you are seeing in these particular images.

As shown, the upper and lower parts of the "dendrite" in the first image do not look like a continuous structure. I would guess that you are looking at a synapse or some other contact between two different processes in the first image. The 3-4'o'clock connection in the loop suggests this interpretation. Can you see vesicles in the images around those connections?

The other dendrite that shows up in your second image might be a glial cell or some other cell's dendrite that participates in the synapse. Alternatively, the other dendrite may just be a chance passing of two dendrites that don't interact functionally.

Of course, it could be that you and the computer have just completely misunderstood the data. My understanding of the Eyewire interface is that the computer guides a lot of the identification and doesn't easily allow you to see the surrounding areas so you can't track structures all the way to their sources. In such a situation, it seems probable that you would end up with ambiguous instances like this that you would have a hard time resolving without more information/expertise. But maybe Seung or one his colleagues can come weigh in on that?

gravity - Is the sphere of influence of our milky way's center super massive black hole same as the Milky way's radius?

No. The black hole at the centre of the Milky way is only a few million solar masses. The same amount of mass, made up mostly of stars, would be enclosed within $sim 10$ parsecs of the Milky Way centre. The bulge of the Milky Way, which is a few thousand parsecs across contains more than 20 billion solar masses.

Thus the dynamics of our Galaxy, outside of the central few parsecs are hardly influenced by the black hole at all.

What holds the Milky Way together? The gravity of everything else - stars, gas, dust, dark matter (the latter probably being the most important once you get to galactocentric radii beyond the Sun).

gravity - Why do Earth and moon move apart but binary black holes move closer?

Here is how the tides move the moon away from the Earth:

The moon orbits the earth, and there is a difference in gravitational force between the the side of the Earth nearest the moon, and the side far from the moon.

This difference in force tends to pull the Earth into a oval shape with its long axis pointing towards the moon.

But the Earth is also spinning, and this spinning moves the axis of the oval forward, so the oval doesn't point towards the moon, but a little ahead of it. So there is a bump on the Earth, and it is permanently a little in front of the moon. This bump has mass and it pulls the moon towards it, So the moon is being pulled forwards. The moon pulls the Earth back. So the Earth's spin is slowed, but the moon gains energy and moves a little further from the Earth.

The moon has also been slowed down to the extent that the same side always faces Earth, and it will remain locked like this.

Gravitational waves, on the other hand, imply an emmision of energy from the binary system, and as energy is lost, the black holes spiral in.

There are no tides on black holes because there is nothing there to be pulled into an oval shape. The event horizon is not a solid surface. The mass of a black hole is concentrated entirely at the singularity, there is no structure to be deformed into a bump.

herbs - How should I harvest Basil leaves as to be least harmful to the plant?

Caveat: I utilise my father's basil rather than growing my own, because he waters more than I do, so his grows bigger, and his is grown in a (waist-high) clump in the ground.

Having said that, I harvest basil by slashing it back. In six weeks or so, I can harvest the same plant again as it resprouts. If I'm being careful, I cut just above a bud to encourage the plants, but when I'm making pesto, I rarely take less than a third of the plant and usually more. I always take off all of the flowers, pinching them out if I don't want to take the stems they're on.

Cutting this way encourages the plant(s) to produce more soft stems full of leaves, which is what you want. A basil plant that is getting leggy needs slashing.

orbit - Can we apply Kepler's law of planetary motion to the moons motion around the earth?

Yes. Kepler's laws apply to orbits of the Earth, and the moon's orbit is elliptical, with an eccentricity of 0.055

Or at least nearly elliptical. In Newton's theory of gravity, if there are two particles in orbit around each other then they will have an elliptical orbit. If there are more than two bodies then the gravity of other bodies will perturb the orbits from exactly elliptical. A more accurate description of the moon's orbit is "Elliptical + perturbations"

The most significant perturbations come from the sun, and from the fact that the Earth is not a perfect sphere. Other planets and tides also have effects on the Moon's orbit.

There are two wiki pages you should read: Orbit of the moon and Lunar Theory

neuroscience - How do dopamine agonists like amphetamine/methylphenidate affect acetylcholine signalling?

Amphetamine and methylphenidate are not (direct) dopamine agonists.

Dopamine agonists are the substances that would specifically bind to dopamine receptors and activate them, thereby mimicking the effects of dopamine release.

Amphetamine/methylphenidate are so-called indirect sympatomimetics. This means that they stimulate the simpatyc nervous systems (with neurotransmitters noradrenaline and dopamine in CNS), but in indirect way: they don't bind to the receptors. Rather, they promote the massive neurotransmitter release from the presynaptic part. The released transmitter (DA, NA) then just diffuses to the postsynaptic membrane and binds to its own receptors.

There are some works done on investigating the effect of these substances on parasympatic system with acetylcholine as neurotransmitter.

Sympatomimetics like amphetamine generally lead to increase of acetylcholine release throurout the nervous system: in hippocampus and caudate nucleus, nucleus accumbens and generally in forebrain and cortex.

This effect of amphetamine is indeed in many cases mediated through dopamine receptors. Same time some direct dopamine receptor agonists were found to supress ACh release in some brain regions.

bioinformatics - Human disease and associated phenotype database?

It seems to me like you're effectively wanting to make a decision matrix.

So... As said above, ICD and SNOMED CT going to have codes for your diseases and symptoms. I'd lean toward SNOMED CT due to the way it organises concepts. Essentially from broad to specific. That way users can enter very specific symptoms, and your matrix only needs to have symptoms as specific as is required.
For example you can say "vomitting" is a symptom of "alcohol poisoning" in your db. And if a user enters "projectile vomitting" the SNOMED structure recognises this as a type of vomitting.

However - Symptoms don't make the disease, and most diseases have a huge array of 'possible symptoms' (Which is why SNOMED CT doesn't have such relationships). So it's not an easy undertaking. Hence why those who've made such db's (as you've linked to) are reluctant to share their IP, at least without $$$.

If you're going to make your own, here's some tips.
Consider:

• only diseases relevant to your use case - eg. Aged care doesn't require paediatric disorders;


• exclude non-specific symptoms;


• rank your symptoms by frequency - eg. 60% of pregnant women have morning sickness, where as 100% have an HCG > 10*

Hope this helps. And good luck.

edit- there is a similar thread on LinkedIn

*fabricated statistic :).

galaxy - Do all the stars visible to the naked eye belong to Milky Way?

For decades the variable star S Doradus, in the Large Magellanic Cloud, was considered to be the most intrinsically luminous star known. But even though the Large Magellanic Cloud is the second or third closest external galaxy, S Doradus is still too far away from Earth to be seen with the naked eye from Earth. O fall the stars that always or sometimes are intrinsically brighter than S Doradus, only the variable Eta Carinae, in our own Milky Way Galaxy, is close enough to Earth that it is sometimes visible with the naked eye.

Omega Centauri, or NGC 5139, was cataloged as a star by Ptolemy in his Almagest about 150 AD and by Bayer in the Uranometria of 1603 - Bayer named it Omega Centauri. It is at a distance of about 15,800 light years from Earth. There is a theory that Omega Centauri is a remnant of a dwarf galaxy that as captured by our galaxy.

Thus Omega Centauri is an object that was listed and named as a star and may be the remnant of a former galaxy that has been captured by our own galaxy. Thus so far it seems to ALMOST fit the definition of an extra-galactic star visible from Earth with the naked (Human) eye.

Of course Edmund Halley noticed that Omega Centauri was not a star as early as 1677. Today it is classified as a globular Star cluster in our own galaxy (and possibly the remnant of the core of a dwarf galaxy). The light that makes Omega Centauri visible to the naked eye on Earth comes from the light emitted by hundreds of thousands or millions of stars, not one single star.

Even though a globular star cluster has the light of tens of thousands to millions of stars, and our Milky Way Galaxy has over a hundred globular clusters, only a few of them are visible from Earth with the naked eye (47 Tucanae mentioned by RichS is another, and it was also mistaken for a single star at first).

So a single star that was as far away as Omega Centauri 15,800 light years away, or 47 Tucanae 17,000 light year away, would have to shine as bright as tens or hundreds of thousands, and maybe even millions, of ordinary stars to appear just barely visible to the naked eye like those two clusters.

The Canis Major Dwarf Galaxy is believed to be 25,000 light years from earth and the nearest external galaxy, if it really is a galaxy. The Saggitarius Dwarf Elliptical Galaxy is about 70,000 light years from Earth and the Large Magellanic Cloud is about 163,000 light years from Earth. A star in the Large Magellanic Cloud, about ten times as far away as Omega Centauri or 47 Tucanae, would have to be as bright as millions to hundreds of millions of ordinary stars to be seen by the naked eye from Earth.

I suppose it is theoretically possible that one of the only about 6,000 stars visible with the naked eye from Earth might actually be in one of the 2 or 3 closest galaxies or floating alone outside of the disc of our galaxy. But it would have to be a supergiant or hypergiant star, and astronomers would have to somehow not notice oddities in its spectrum that would point to it being so rarely luminous.

I would estimate that the odds against that would be "astronomical".

observation - How to calculate the LST of an astronomical object at a given height above the horizon [in degrees]?

My situation:

I want to observe M52 at RA = 23h24m48s, DEC = +61deg35arcmin36arcsec from, let's say, Calar Alto at 37.23deg N and 2.546deg W.

How can I calculate the Local Sidereal Time (LST) at which M52 is at 40degrees height above the horizon?

Thank you for your help!

ascension - How to find maximum and minimum right acsension and declination based on the telescope's location?

In the Southern hemisphere, the maximum declination you can see is
90-L where L is your latitude. The minimum is -90, since you can see
the south celestial pole.

As the earth rotates and revolves, you can see any right ascension
within those declinations.

The only exception is that you ordinarily can't see stars that are too
close to the Sun. However, the Sun moves enough between October and
March that all right ascensions will be visible at night sometime
between October and March.

genetics - What's the aim of genetically modifying of foods/organisms?

GMO foods have a huge potential to make food cheaper to produce and more nutritious.

The most common GMO foods have at least one gene added to them - an enzyme that makes the plant resistant to RoundUp - an herbicide made by the same company (Monsanto). this makes the farmers able to grow their crops with much less intensive labor to keep the plants healthy. It does cost some money and people wonder whether using so much roundUp is good. I won't come down on the benefits of this, but you can see how it might be more economical way to grow crops. roundUp is biodegradable and does break down in about 3 weeks, just FYI.

Other GMO foods can make the crops more resistant to drought, disease or insects. This might enable crops to be grown in areas and or with longer growing seasons - a big advantage for thirsy crops like tomatos or rice. Other GMO project may allow us to make the crops more nutritious. A famous example of this is golden rice, which has been enhanced to produce pro-vitaminA, which will help malnutrition in millions of children who can die annually because of a lack of vitamins in their diet.

There is also an effort in nutriceuticals, where vaccines and common drugs maybe produced by edible plants for easily processing or even direct distribution of pharmaceuticals.

For people who can afford organic food and free range beef, I think its great that its available, but at for a hungry world, GMO foods can help solve some vital problems.

radio astronomy - Why (actually) aren't ground-based observatories using adaptive optics for visible wavelengths?

Adaptive Optics (AO) techniques allow ground based observatories to dramatically improve resolution by actively compensating for the effects of Astronomical Seeing.

The atmospheric effects are quite variable in both time and location. A parameter called Isoplanatic Angle (IPA) is used to express the angular extent over-which a given wavefront correction optimized for one point (usually a guide star, artificial or natural) will be effective. As an example, Table 9.1 in this Giant Magellan Telescope resource shows values for IPA scaling almost linearly (actually: $simlambda^{6/5}$) from 176 arcseconds at a wavelength of 20 microns to only 4.2 arcseconds at 0.9 microns.

This suggests an IPA of 2 to 3 arcseconds for visible wavelengths, which taken by itself is not a killer limitation.

However, it seems almost all currently active AO work is done exclusively in various infrared wavelengths, apparently down to 0.9 microns but no further. (AO is also implemented computationally to array data in radioastronomy.)

Is this because the observed wavelength needs to be longer than the guide star monitoring wavelength? Because it is simply much harder and there is always Hubble above the atmosphere for visible work so it's not worth the extra effort, or is there another more fundamental reason?

I'm not looking for speculation or opinion, I'd like a quantitative explanation (if that applies) - hopefully with a link for further reading - thanks!

probe - How will Yuri Milner and Stephen Hawking's nanobots decelerate and transmit data upon arrival at Alpha Centauri?

Solar sails often suggest a couple of modes for slowing down.

1) Have a launch laser at the target location to slow it down the same way. Assumes much infrastructure.

2) Use the solar energy of the target sun to slow the sail down. I.e. Turn it around and spend a longer time decelerating as you get closer and closer.

3) There was a model, where the main sail had a second larger sail that would fly with it, during acceleration, but upon cruise would separate, and advance in front of the main sail. Then the launch laser would target the larger sail, to reflect the energy back on the smaller sail to slow it down. (Lots of tricky bits in that approach).

black hole - Large hadron collider

Even if the LHC did create a black hole, its mass would be no greater than the sum of the particles that formed it, i.e. very tiny. It would evaporate almost instantly due to Hawking radiation. Secondly, subatomic particles have been colliding with atoms high in earth's atmosphere for eons, and we're still here.