Astrophysics and Cosmology - Discuss the Universe here

[Agent : Orange]

How do they know they are so small - is it based on theory or observation?

Both. They are predicted to have a range of masses, the most naive theoretical estimates say up to three solar masses. The largest observed neutron star is around two solar masses (http://www.telegraph.co.uk/science/space/8091209/Biggest-neutron-star-ever-detected-is-twice-the-mass-of-the-sun.html), and a variety of estimates put the radius between 10 and 12 km. There are a number of binary systems where neutron stars live that have given good measurements of both the mass and radius, but magnetars so far have always been solitary.

Neutron stars in general are interesting. When they are seen as pulsars, they were first thought to be evidence of an alien signal! In fact the first known pulsar was designated LGM-001 where LGM stood for Little Green Men, and were seriously considered a possibility for first contact until other examples of them were seen. To this day pulsars provide extremely accurate pulses, enough to be used as precise timekeeping devices.

Do they give off any light other than xrays and gamma rays?

Most pulsars (neutron stars) are known from their radio properties and magnetars are no different, they also give off radio emissions in most cases as well, see  (http://www.nrao.edu/pr/2006/radiomagnetar/) and (http://www.sciencedaily.com/releases/2013/08/130814132319.htm).

So what would the damage be if we were hit by one of these blasts from the closer ones? 

We'd get a blast of gamma and X-rays, so very similar to what Kaku described from WR104... it would be "bad" for our planet.

According to the wikipedia article, after 10,000 years their strong magnetic fields have decayed - do they still pose a threat after such time?  Do we know how old these ones that are close to us are?

It's thought that once they enter this period they no longer display magnetar properties if our current understanding is correct. It's when such huge fields are present there are potential problems.

What do you have to say about SGR 1900+14, the one that has a ring of matter around that... WTF?  Did magnetism draw the matter in, or gravity from the star?  How would that happen?  I know wikipedia says it's unknown, but are there any guesses?

Super interesting, here's an image of the ring with article as well (http://news.softpedia.com/news/Weird-Ring-Around-Magnetar-Leaves-Astronomers-in-a-Dillema-86781.shtml). In fact there are a number of such structures around ordinary pulsars so such a thing is not totally unheard of. The material that was expelled when the massive progenitor star collapsed becomes "fall-back material" that makes up the ring, so it's all due to gravity.

But no one really knows what to expect when it comes to magnetars. Some people question if they are neutron stars at all, and the argument exists these things may be even denser objects known as quark stars.

Your link talks about the degenerate matter state of what these guys are made of - something like a solid, but like a gas as well.   If you had to guess what landing on this stuff would look/feel like if you could get close to it, how would you describe it?

It's a solid mass of pure neutrons. You can think of a white dwarf (0.5-1.5 solar masses) as being like a giant atom, in these stars the electron cloud of each atom can be thought of as overlapping so the electrons are free to run around through the entire star. These stars resist further collapse as white dwarf stars and they are made of electron degenerate matter. When you increase the mass even the atoms are forced together and a process called inverse beta decay occurs in which (basically) the electrons are forced into the protons in the nucleus making an abundance of neutrons. In stars that are 1.5 solar masses or more the electron degeneracy pressure is not enough to overcome the crunch of gravity, and then you get a neutron star. For stars that have more than something like 3 solar masses, even the neutron degeneracy can't hold up against gravity and a black hole is made. On a neutron star, a square centimeter of surface has the energy of something like a years worth of power from a nuclear reactor, and a square meter emits more energy than humans have ever produced. So the environment of these guys is extremely energetic, and not anything like where you would want to be. The surface of a neutron star is one of the most smooth in the universe, and a centimeter sized lump is like a mountain on their surface. Also due to the high mass and small radius, it means time behaves strangely - what would seem to you just a few minutes on the surface could mean years or more to an outside observer.

Our own Sun will end up as a white dwarf (electron degenerate) star, which means it will be the least massive compact object that can be formed. But that on it's own is still pretty badass:

[Mind Flayer Monk]

Do all black holes have the same gravity, or does it differ based on the black hole?

[Agent : Orange]

Do all black holes have the same gravity, or does it differ based on the black hole?

Depends on the mass of the black hole and your distance from it. We know of black holes that are star-sized and those that are much larger - in some cases up to a billion times the mass of the sun - that live at the center of galaxies. This is the reason the distant quasars are so bright, those galaxies (or AGN - Active Galactic Nuclei) have big black holes at the center that are eating up matter.

But black holes are not like vacuum cleaners. If you were to transform the Sun into a black hole right now all of the planets would continue to orbit around as usual and nothing about their paths around the "sun" would change except of course we'd get no light from it. This is because all of the Sun's mass is still there, just in a much smaller volume. This is one thing the popular culture has gotten very wrong about black holes.

[area51drone]

Agent, I feel like you're our "on call physicist."   LOL.  I hope I don't Jazmunda you away from answering questions.   I promise I will make all this worthwhile to you somehow though.  Thank you for your answers, as always. 

Okay, so in layman's terms, if we got hit from a magnetar event, life on this planet would end as we know it?   How long would the event last?  Is it possible that maybe 1/4 of the planet would not be hit with the event and still survive, or would it shave off our atmosphere or just burn and irradiate everything on the surface?   Come on man, if we're talking doomsday, we need some more detail!

You missed the question about knowing how old any of these magnetars near us are - do we have any idea?

And lastly, so basically, neutron (and magnetar) stars are almost like one huge Avogadro sphere, just made instead of pretty much the largest atom known to mankind?
http://en.wikipedia.org/wiki/Kilogram#Avogadro_project

[Mind Flayer Monk]

Depends on the mass of the black hole and your distance from it. We know of black holes that are star-sized and those that are much larger - in some cases up to a billion times the mass of the sun - that live at the center of galaxies. This is the reason the distant quasars are so bright, those galaxies (or AGN - Active Galactic Nuclei) have big black holes at the center that are eating up matter.

Does anyone keep this data in a publicly available data set? Black Hole, location, estimated mass, distance?
If not seems like a pretty cool resources to make available to the public.

[area51drone]

Depends on the mass of the black hole and your distance from it. We know of black holes that are star-sized and those that are much larger - in some cases up to a billion times the mass of the sun - that live at the center of galaxies. This is the reason the distant quasars are so bright, those galaxies (or AGN - Active Galactic Nuclei) have big black holes at the center that are eating up matter.

But black holes are not like vacuum cleaners. If you were to transform the Sun into a black hole right now all of the planets would continue to orbit around as usual and nothing about their paths around the "sun" would change except of course we'd get no light from it. This is because all of the Sun's mass is still there, just in a much smaller volume. This is one thing the popular culture has gotten very wrong about black holes.

Once these super massive black holes (as I believe they are called) at the centers of galaxies have eaten all the matter that's within arm's reach, how long will it take for Hawking radiation to dissolve them - or will they ever be dissolved?   Just in general terms of time, I mean - millions of years?  Billions?  Trillions?

[area51drone]

Does anyone keep this data in a publicly available data set? Black Hole, location, estimated mass, distance?
If not seems like a pretty cool resources to make available to the public.

I can answer this one..   Here's a list.

http://en.wikipedia.org/wiki/List_of_black_holes

[Agent : Orange]

Agent, I feel like you're our "on call physicist."   

My endgame has been reached. Now that I've achieved this goal there's nothing left for me but "sewerpipe".
Seriously though I sit here hitting "refresh" waiting for new comebacks so there you go, that makes me happily "on call".

Okay, so in layman's terms, if we got hit from a magnetar event, life on this planet would end as we know it?   How long would the event last?  Is it possible that maybe 1/4 of the planet would not be hit with the event and still survive, or would it shave off our atmosphere or just burn and irradiate everything on the surface?   Come on man, if we're talking doomsday, we need some more detail!

To be honest I'm not quite sure.

The bursts are quick, meaning that they're more like pulses and last at most a few seconds. Gamma ray bursts last for much longer and can spit out much more energy. But the thing which impresses me the most is that the response of the atmosphere has been measured for a magnetar flare and at great distance. I shudder to think what would happen if a much closer magnetar bursted like the 1979 event. In that case I think it would be very bad, but I'm not willing to speculate if that would be enough to scrub the Earth. It would definitely affect us. Think about this, WR104 is 8000 ly away. SGR 0418 is only 6500 ly away but may be able to emit a flare with total power equal to that which the Sun puts out in a year. The most powerful flux of gamma rays from outside our solar system has been from magnetar flux and not GRB.

You missed the question about knowing how old any of these magnetars near us are - do we have any idea?

This is a really interesting research question.

We have best guesses, but no one really takes these too seriously. The simplest picture assumes magnetars have magnetic fields that are dipolar like bar magnets. That's not to say it's the whole picture but more like a rough overview which makes sense for stars like the Sun. But again, one should always take these things with a grain of salt when it comes to magnetars. The dipole picture lets us calculate an age for the object which can be found here for example:
http://www.physics.mcgill.ca/~pulsar/magnetar/main.html
under "tau_c". But this is the simplest picture and you'll notice some of the entries in this table have longer lifespans than you might expect, telling us maybe the simplest picture isn't good enough. I would argue that is the case and the best we can do is speculate.

And lastly, so basically, neutron (and magnetar) stars are almost like one huge Avogadro sphere, just made instead of pretty much the largest atom known to mankind?
http://en.wikipedia.org/wiki/Kilogram#Avogadro_project

Think of a white dwarf as a giant atom, and a neutron star like a giant nucleus. Not quite an accurate picture but close enough to get the significance across.

[Agent : Orange]

Does anyone keep this data in a publicly available data set? Black Hole, location, estimated mass, distance?
If not seems like a pretty cool resources to make available to the public.

I'm sure such a thing exists, but I don't know where. Maybe you can find some details on the web?

The problem about making such a catalogue is that there are many - now thousands - of active galactic nuclei known. These are the most massive (thousands of times the mass of the Sun) black holes known. There are many more small ones out there. I really doubt anyone has collected and categorized both types in a single reference.

EDITED TO ADD:

I can answer this one..   Here's a list.

http://en.wikipedia.org/wiki/List_of_black_holes

I got pwned! Here they are apparently!

[Agent : Orange]

Once these super massive black holes (as I believe they are called) at the centers of galaxies have eaten all the matter that's within arm's reach, how long will it take for Hawking radiation to dissolve them - or will they ever be dissolved?   Just in general terms of time, I mean - millions of years?  Billions?  Trillions?

Hawking radiation is a pretty inefficient process unless you're talking about very small black holes. The big guys (meaning solar mass or more) can stay quiet for billions of years without completely evaporating

[area51drone]

Seriously though I sit here hitting "refresh" waiting for new comebacks so there you go, that makes me happily "on call".

And I hit refresh every few minutes looking for new answers!  A match made in the heavens.   

Think of a white dwarf as a giant atom, and a neutron star like a giant nucleus. Not quite an accurate picture but close enough to get the significance across.

I got nothing else right now, but I do mean to get to the bottom of this - so both are very smooth, but how would you characterize the "material"?   I mean, is there anyway to say "it would be metallic looking" or "just a glowing light"  or "dark and slippery."   

I also want to know what its like as you delve into the depths of Jupiter's atmosphere.  Will you eventually hit an ocean made of gas?    I realize that these are questions that are completely hypothetical, but they are so interesting to me.

[area51drone]

Alright, I got another one for you Agent - since they first detected the CMB, have they noticed it change at all?     Shouldn't the temperature/levels go down as the radiation continues to spread into mass and especially as space expands?

[Agent : Orange]

I got nothing else right now, but I do mean to get to the bottom of this - so both are very smooth, but how would you characterize the "material"?   I mean, is there anyway to say "it would be metallic looking" or "just a glowing light"  or "dark and slippery."   

Going to be glowing really bright in all kinds of radiation but with an excess of gamma and X-ray. So expect it to be bluer than anything you've ever seen before if you're standing on it. And neutron degenerate matter is denser than iron so maybe that will help. It's going to be really bright and very smooth. That's about the best I can do. And time will behave strangely too.

I also want to know what its like as you delve into the depths of Jupiter's atmosphere.  Will you eventually hit an ocean made of gas?    I realize that these are questions that are completely hypothetical, but they are so interesting to me.

Actually you're right in some sense, at some depth you will find metallic liquid hydrogen. This won't be like an ocean on Earth but will happen gradually as you descend through the layers of the planet, things just get naturally more dense. Hydrogen should be packed so tight near the center it behaves as if molten, and maybe more than that (http://www.universetoday.com/105420/jupiter-and-saturn-may-be-rich-in-diamonds/).

[Agent : Orange]

Alright, I got another one for you Agent - since they first detected the CMB, have they noticed it change at all?     Shouldn't the temperature/levels go down as the radiation continues to spread into mass and especially as space expands?

You don't expect the CMB to change as it was emitted a "short" time after the big bang. Actually it's seen to be gravitationally lensed by significant masses between us and the last scattering surface that emitted the CMB and also by scattering due to material in galaxy clusters (Sunyaev-Zeldovich effect), both effects of which have been seen. But the radiation itself was released a long time ago so anything that affects it occurs between us (the observer) and the point of emission (300,000 years after the big bang).

[area51drone]

You don't expect the CMB to change as it was emitted a "short" time after the big bang. Actually it's seen to be gravitationally lensed by significant masses between us and the last scattering surface that emitted the CMB and also by scattering due to material in galaxy clusters (Sunyaev-Zeldovich effect), both effects of which have been seen. But the radiation itself was released a long time ago so anything that affects it occurs between us (the observer) and the point of emission (300,000 years after the big bang).

Hmm..  I initially responded by saying "I see, so it's just like light from distant galaxies, correct?"  But it is uniformally around us.  So I don't get it then.   How can it have a point of emission yet be all around us?    If it had a point of emission, then eventually as the universe continues to grow, we won't see it, just as Kaku says the universe will be a very cold lonely place.   Won't it become more "dim" over time then?

[Agent : Orange]

Hmm..  I initially responded by saying "I see, so it's just like light from distant galaxies, correct?"  But it is uniformally around us.  So I don't get it then.   How can it have a point of emission yet be all around us?    If it had a point of emission, then eventually as the universe continues to grow, we won't see it, just as Kaku says the universe will be a very cold lonely place.   Won't it become more "dim" over time then?

The big bang does not have a center, since all of space-time come from that event. By looking out at great distances we look farther back in time. So when we look in any direction on the sky at microwave frequencies we can see the afterglow of the big bang as the cosmic microwave background. When the universe was small, this field of radiation was super intense. But as the universe expanded the wavelength of the radiation was stretched out and the temperature dropped. Eventually when it became cold enough the primordial plasma became neutral material (mostly hydrogen) and the CMB was free to propagate forever. The CMB we see now has a temperature of 2.75 kelvin, and that's entirely due to the expansion of the universe.

[area51drone]

The big bang does not have a center, since all of space-time come from that event. By looking out at great distances we look farther back in time. So when we look in any direction on the sky at microwave frequencies we can see the afterglow of the big bang as the cosmic microwave background. When the universe was small, this field of radiation was super intense. But as the universe expanded the wavelength of the radiation was stretched out and the temperature dropped. Eventually when it became cold enough the primordial plasma became neutral material (mostly hydrogen) and the CMB was free to propagate forever. The CMB we see now has a temperature of 2.75 kelvin, and that's entirely due to the expansion of the universe.

I can wrap my mind around the CMB being all around us, and at a temperature it is at now.  What I can't grasp is why the temperature won't drop as the universe expands.   That temperature is energy, correct?   As space expands, why wouldn't that dissipate the energy over more space?

[Heather Wade]

The big bang does not have a center, since all of space-time come from that event. By looking out at great distances we look farther back in time. So when we look in any direction on the sky at microwave frequencies we can see the afterglow of the big bang as the cosmic microwave background. When the universe was small, this field of radiation was super intense. But as the universe expanded the wavelength of the radiation was stretched out and the temperature dropped. Eventually when it became cold enough the primordial plasma became neutral material (mostly hydrogen) and the CMB was free to propagate forever. The CMB we see now has a temperature of 2.75 kelvin, and that's entirely due to the expansion of the universe.

So, it's true that in a gazillion years, there will be no stars because they will have all slowly faded away, due to this expansion?

Though, I often wonder which will happen first:  Our sun going supernova, or the last star fading into the black of space?

Forgive me for chiming in...   

[Mind Flayer Monk]

I found a dataset-Carnegie Mellon maintains one-its 2gb of SQL lite. So sounds like there is mountains of data out there for this.
The download link to the set is broken so I will contact CMU tomorrow.
Actually a pretty cool page overall, thanks for the inspiration with the questions and answers.

http://www.pdl.cmu.edu/AstroDISC/massive-black.shtml

[area51drone]

Agent - in that video I posted of the recent Carroll talk (the hour long NSF one), at 35:00 roughly he's talking about the Bullet Cluster and how this is a white crow for dark matter existing because the mass of the galaxies should have been in the gas, not in the galaxies themselves.  How can he be sure of this?  He mentions they have a method of determining this by the matter of the gas being heated and giving off x-rays.   But is it not possible for the galaxies to have multiple SMBH's or some other massive objects that have more mass than the gasses left over from the collision?  I understand he has to gloss over this stuff, but it's like saying "christ is god because the bible says so."   How do you know if the bible is correct... see what I'm saying?

[Agent : Orange]

I can wrap my mind around the CMB being all around us, and at a temperature it is at now.  What I can't grasp is why the temperature won't drop as the universe expands.   That temperature is energy, correct?   As space expands, why wouldn't that dissipate the energy over more space?

It will drop. My point was it has dropped since it was first emitted due to the expansion. It is now 2.75 kelvin, it was much more intense when it was emitted.

[Agent : Orange]

So, it's true that in a gazillion years, there will be no stars because they will have all slowly faded away, due to this expansion?

Though, I often wonder which will happen first:  Our sun going supernova, or the last star fading into the black of space?

Forgive me for chiming in...   

The expansion will only redshift cosmological objects like other galaxies. So we will see all objects outside our galaxy recede from us. For objects within our own galaxy, our Sun will go nova first sadly. Means we need to get ourselves out there and used to exploring.

[Agent : Orange]

I found a dataset-Carnegie Mellon maintains one-its 2gb of SQL lite. So sounds like there is mountains of data out there for this.
The download link to the set is broken so I will contact CMU tomorrow.
Actually a pretty cool page overall, thanks for the inspiration with the questions and answers.

http://www.pdl.cmu.edu/AstroDISC/massive-black.shtml

Sounds like this is the result of a simulation and not an actual observed data set. Super interesting, but proceed with caution!

[Agent : Orange]

Agent - in that video I posted of the recent Carroll talk (the hour long NSF one), at 35:00 roughly he's talking about the Bullet Cluster and how this is a white crow for dark matter existing because the mass of the galaxies should have been in the gas, not in the galaxies themselves.  How can he be sure of this?  He mentions they have a method of determining this by the matter of the gas being heated and giving off x-rays.   But is it not possible for the galaxies to have multiple SMBH's or some other massive objects that have more mass than the gasses left over from the collision?  I understand he has to gloss over this stuff, but it's like saying "christ is god because the bible says so."   How do you know if the bible is correct... see what I'm saying?

I have to get back to you on this, need to get some sleep for now
But the answer involves some very interesting physics.

[area51drone]

Goodnight, sweet prince.  Oh, that was RCH. Sorry.  'Night Agent!

[area51drone]

It will drop. My point was it has dropped since it was first emitted due to the expansion. It is now 2.75 kelvin, it was much more intense when it was emitted.

Understood, glad we are on the same page.  Back to my question - has it been observed to drop any amount since the discovery?

[Agent : Orange]

Understood, glad we are on the same page.  Back to my question - has it been observed to drop any amount since the discovery?

We haven't been observing it for nearly long enough, and we can only measure differences of 1/100,000th of a degree. The temperature will stay pretty much constant except over cosmic time scales so we don't expect to see any temperature change.

[West of the Rockies]

Just a suggestion for those unfamiliar with National Public Radio (NPR).  They have had a long-running program on Fridays called Science Friday (formerly Talk of the Nation:  Science Friday).  Where I live, we get two hour-long back-to-back episodes.  The origins of the universe and cosmology are frequent subjects.  If you want to hear informed (yet still speculative) discussion on these subjects, surf on over to the NPR.org website and look up the archived episodes.

[Agent : Orange]

Just a suggestion for those unfamiliar with National Public Radio (NPR).  They have had a long-running program on Fridays called Science Friday (formerly Talk of the Nation:  Science Friday).  Where I live, we get two hour-long back-to-back episodes.  The origins of the universe and cosmology are frequent subjects.  If you want to hear informed (yet still speculative) discussion on these subjects, surf on over to the NPR.org website and look up the archived episodes.

Cool, never heard this before. Thanks for the suggestion.

[area51drone]

I have to get back to you on this, need to get some sleep for now
But the answer involves some very interesting physics.

I bet!  And couldn't it be that some gas clouds are thin, such that they don't have a lot of mass but still reflect light back at us?