Pulsar SMASH!

By Phil Plait | October 16, 2008 12:15 pm
Illustration of a pulsar

It’s a (Bruce) banner moment for NASA’s new Fermi satellite: it’s found a pulsar that emits only gamma rays.

Brief background: when a massive star explode, its core collapses. If it has enough mass, the core shrinks down into a black hole. If it doesn’t have quite that much oomph (if it has about 1 – 2.8 times the mass of the Sun) it forms a weird object called a neutron star. As massive as a star but only a few kilometers across, a neutron star is incredibly dense, rapidly rotating, and has a magnetic field intense enough to give you an MRI from a million kilometers away.

OK, I made that last one up, but in fact it sounds about right. The point: neutron stars are seriously awesome, right on the edge of matter as we understand it.

The supercharged magnetic field channels a tremendously powerful flow of energy away from the star in twin beams like a lighthouse. And, like a lighthouse, as the star rotates these beams sweep around. If they’re aimed at Earth we see a pair of pulses every time the star spins around once. So, duh, we call these special neutron stars pulsars. You can see a way cool animation of this on NASA’s Conceptual Image Lab web page.

Usually, the beams from these pulsars contain light from all (or nearly all) across the electromagnetic spectrum. We seem them in radio waves, visible light, ultraviolet, even X-rays and some in gamma rays. The processes that create these beams are pretty fierce and weird, and the type of light emitted depends on the process. However, in general, if we see high energy light (like X- and gamma rays) from a pulsar, we tend to see it in lower energy light (optical and radio) as well.

But Fermi found an oddball! Located about 4600 light years away in the constellation of Cepheus, CTA-1 is a supernova remnant, the expanding debris from an exploding star. But that expanding junk is only from the outer layers of the detonated star: the core collapsed down into a neutron star, and that’s what Fermi detected. This newly discovered gamma-ray-only pulsar spins three times per second — think on that; an object with the mass of an entire star spinning at that rate! — and is blasting out gamma radiation with 1000 times the Sun’s entire energy output.

And all of it in super-high energy invisible gamma rays. The Hulk has nothing on this pulsar.

Actually, let’s pause for just a sec. Is it sunny outside? Good. Go outside, and hold your hand up. Feel the warmth? That’s just a bit of optical light warming your hand. Now think about how much energy is falling over the entire Earth itself, a gazillion times the size of your hand. Now think about how much energy the Sun is emitting in all directions; the entire Earth only intercepts about one-two billionths of that light. Now think about one thousand times that much energy. Now think of all that energy being only in the form of DNA-shattering gamma rays.

Yeah, now you’re getting it. This object is seriously freaky.

We know of about 1800 pulsars, and all of them emit radio waves. All but this guy. It’s a brand new category of object (well, a sub category, but still), a new character on the cosmic stage. But why does it only emit gamma rays? Hey, good question. I don’t know the answer (and the press release doesn’t say, in fact). I suspect the answer right now is, we don’t know. This object was only discovered a little while ago, and worse, gamma rays are really difficult to study. That’s why we launched Fermi in the first place! Worse even than that, without being able to look at this object in radio, optical, or any other form of light really hobbles our ability to study it.

For now, I think we’ll have to rely on Fermi’s observations and then look at theoretical models. I imagine there will be astronomers all over the world pouncing on this, trying to figure out how the magnetic fields of the star can be so choosy (maybe they’re elitist).

But until then, as usual, I have to wonder: if we only just now found this object, what the heck else is floating around out there just waiting for us to find?

Pulsar image credit: NASA.

CATEGORIZED UNDER: Astronomy, Cool stuff

Comments (57)

Links to this Post

  1. Pulsing with gamma-rays : Stochastic Scribbles | October 16, 2008
  1. But it’s cloudy outside… And isn’t it more than just “optical light” warming your hand? I know the atmosphere blocks a lot of the energy, but still quite a bit gets through.

    And your last question is why I keep coming back here! What else will we find?

  2. Cheyenne

    Crazily cool post.

    I wonder if I can get one of these on eBay. You can find meteorites after all.

    It would be a nice conversation piece for the living room. All I’m saying….

  3. Jeremy

    How can we say ‘only gamma’ if we don’t have a way to see anything but gamma?

  4. Brando

    Hmm, sounds like a black hole…but it’s not. What a quandary?

  5. Chris A.

    Isn’t it more likely that the pulsar’s radio/IR/optical/UV/X-ray flux is not totally absent, but merely too weak to detect with current instruments? Nature abhors a (macroscopic) non-blackbody, after all. So perhaps the questions should be: Can we detect [b]any[/b] non-gamma emission if we bring big enough instruments to bear (has Keck looked yet? how about a long exposure from HST, once it’s up and running again?), and, is there a mechanism that could somehow be enhancing the gamma emission and/or suppressing the non-gamma? (I’m inclined to think the latter.)

  6. Ryan

    Neutron stars are nifty. Careful though, or the tides’ll getcha.

  7. Todd W.

    Phil, a little heavy handed with the pun, no? However, I am green with envy that you can get away with it. :)

  8. Helioprogenus

    Perhaps the energy released is related to the density of the pulsar. Not all pulsars are the same density, and perhaps this one was near the threshold of a black hole. Perhaps it missed it’s black hole calling by only a few percent and thus, this super-ultra-immensely dense pulsar is somehow emitting gamma rays because of it. Is any of this theoretically possible?

  9. The hypothesis was put forth that the gamma radiation is broader than the radio sources, so perhaps the radio emissions are not pointed in our direction, but the gamma-rays are?

  10. Tim G

    Just how much more energetic are these gamma rays than the rays emitted from an x-ray pulsar? Could gravitational contraction account for the energy source of this pulsar like it does for x-ray pulsars?

    P.S.
    I checked my mail today and guess what?
    I got mine!

  11. Sili

    Could it be that that expanding cloud from the explosion somehow serves to block out most of the other kinds of radiation?

  12. DGKnipfer

    Perhaps we’ve caught a Black Hole in the process of forming? Wouldn’t that be cool? I wonder if it will still emit Gama Rays in a few thousand years?

  13. Bobcloclimar

    Clearly, the pulsar is surrounded by a Dyson sphere that provides inadequate gamma-ray shielding.

  14. dre

    Pulsars, I suppose by definition, have magnetic poles that do not line up with their rotational poles. Why don’t the poles coincide? Are there neutron stars stably beaming energy from their aligned magnetic/rotational poles that are therefore not pulsars?

  15. One reason I love this blog so much is that the comments are often as interesting and informative as the posts :)

  16. JoeSmithCA

    I wonder whats going inside a neutron star. What’s the material inside the star doing? Questions, questions, questions.

  17. DrFlimmer

    AFAIU, if we don’t see the beam of a pulsar, we think it’s a normal neutron star (but I must say, the word “normal” seems somehow misleading ;) ).
    I think it would really be a coincidence when the magnetic and the rotational poles are the same (they are even not for the earth!). Because of “conservation of angular momentum” the rotational axes of the newborn neutron star and the previous star are the same. But the magnetic field of a star is wiered (every sun spot is a pole itself), so the resulting field seems surprisingly simple to me (I don’t know if it’s just our model or if the picture Phil used has been confirmed). But as we see, the magnetic field can but doesn’t have to line up with the rotation.

    Well. The detection of a “pulsar” with aligned poles seems unlike to me, because we would have seen one ;) . I mean, it would be a tremendous light source (because all of it’s light would be shining right in our face) and would have been spot easily, but I don’t know about any of such a bright source; or it would be undetectable and just named as a “normal” neutron star.

  18. DrFlimmer

    That first one goes to dre ;)

    This second one is for JoeSmithCA:

    There are some speculating that inside a neutron star there could be a quark-gluon-plasma or even free quarks floating around due to the high pressure. But sadly: we do not know (as always ;) ), but trust me, we would really love to know!!!!
    On the surface we can be quite sure that there es thick layer of neutrons packed as dense as a nucleus.

    But you are right: Questions over questions.

    I have one, too:
    Is it possible that a neutron star doesn’t collapse into a black hole due to its rotation? That he would be too massive to stay as a neutron star and only the centrifugal force keeps the neutron star alive? And with a little less angular momentum he would finally collapse?

    There are many “milli-second” pulsars (and they are more accurate with their timing than our best atomic clocks!!) out there… they are really rotating up to 1000 times a second (ONE THOUSAND TIMES A SECOND!!!!!!), maybe one of those guys could be such a near-by-black-hole ;)

  19. Paul M.

    There really is some weird and interesting stuff up there… sounds almost like DeathfromtheSkies!

  20. Wildride

    I would tend to wonder how much the pre-ejection mass has to do with it. Does the additional material block everything else in the case of a massive original star, or are the other forms of radiation second hand from the interaction with the ejected matter?

  21. How does a gamma ray telescope achieve focus?

  22. Ian

    I’m curious whether anyone has calculated what the rotational period of the sun would be if it were compressed to the size of a neutron star and retained its angular momentum (I tried to work this out myself, but it’s too complex for me).

    Also: do black holes rotate? On the one hand, with a smaller radius, they should rotate even faster than neutron stars. On the other hand, the weirdness that is the event horizon would seem to prevent them from ever actually completing a rotation.

  23. MarkH

    Got it, got it, got it….:) Death From the Skies was in my mailbox when I got home… woohoo

    I wonder if something like this pulsar is in the book. guess i’ll have to read it (giggle).

  24. Anne

    A correction: in most pulsars you only see one pulse per rotation. If the magnetic axis is at right angles, or nearly, to the spin axis, then you’ll see two (and in some cases we do; the weaker is called an “interpulse”), but if the angle is less than ninety degrees we might only ever see one of the poles.

    We actually know many X-ray pulsars with no optical or radio emission; the one called “Geminga” was the prototype (though there was a disputed detection of radio pulsations by a Russian group).

    Chris A.: it probably is emitting *some* X-rays, optical, and radio. But people have looked at that supernova remnant before in the X-rays, and the authors of this paper searched through all those observations and didn’t find any pulsations or even a non-pulsating point source. (The data from X-ray observations becomes public a year after it is taken; you could go download it if you wanted to.) It probably hasn’t been looked at in optical (for pulsations, I mean) because cameras that are sensitive enough to do astronomy with and fast enough to see a pulsar pulsate are hard to come by. It can be done, but it’s a lot of work and people only do it when they know there’s a pulsar there. So probably somebody’s going to look now; who knows what they’ll find?

    Helioprogenus: we think all young pulsars emit gamma rays to some extent. What determines how bright a young pulsar is is not so much the density as its spin frequency and its magnetic field. If it’s spinning fast and/or has a high magnetic field, it’ll slow down rapidly, and all that rotational energy it’s losing goes into various kinds of emission. Exactly what determines how much energy goes into gamma rays and how much into X-rays and how much into a near-lightspeed wind of particles is unknown. In fact, we’re pretty unclear about even *where* in a pulsar’s magnetic field the radiation is generated. But Fermi is hopefully going to help clear that up for us.

    DrFlimmer: I think, though I’m not sure, that a neutron star kept from collapsing only by rotation would be unstable. That is, if you gave it a little push, say squashing it at the poles, the rapid rotation and high gravity would tend to amplify the distortion, leading to a runaway process tearing the star apart. Which sounds dramatic and impressive, but it would happen during the formation of the star – in the middle of a supernova – where there’s so much else going on you’d never see it.

    Wildride: By several hundred or several thousand years later, like this guy, the tremendous energy of the supernova explosion has pretty much cleared out the neighborhood. In fact the pulsar it self often drives a “pulsar wind” consisting of electrons and anti-electrons (positrons) which sweeps the neighborhood further. We can often see the shock fronts where these streams of rapidly-moving material crash into slower-moving material, like the interstellar medium. That’s what the Crab Nebula is. So we don’t think that this one is being blocked by its ejecta. For very young pulsars it’s a different story: for example for supernova 1987A, we think it should have generated a compact object, either pulsar or black hole, but nobody can find it. One hypothesis for why we can’t is that it’s still surrounded by junk.

  25. Tod

    @Phil “I have to wonder: if we only just now found this object, what the heck else is floating around out there just waiting for us to find?”

    And that is the wonderful thing about being alive – learning about the discovery of things that are stranger than fiction. Thanks for the writ-up, Phil. I love this blog.

    @Mike Torr “One reason I love this blog so much is that the comments are often as interesting and informative as the posts :)”

    Mike, I’m with you all the way on this one! I sometimes feel like the class dullard who’s wandered into an AP course with all the high energy coming from subsequent comments.

    -Tod

  26. Anne

    LabLemming: For X-rays you can actually make mirrors, but they only reflect at very shallow angles, so you use the nearly-tubular section of a paraboloid and have a very long telescope. For higher energy gamma rays (like Integral’s SPI, around 1 MeV) you often use a “coded-mask” arrangement: basically a pinhole camera. Only pinhole cameras don’t let in much light, so you use lots of pinholes. This scrambles your image, but with enough cleverness you can unscramble it. But at the energies Fermi sees – 100 MeV or so – the photons come in one by one and they crash right through materials for some distance. So you build a detector with several layers; you detect the photon position in each layer, and then connecting the dots you find out what direction it came from. So Fermi doesn’t really focus gamma rays at all.

  27. Ijon Tichy

    LL asked:

    How does a gamma ray telescope achieve focus?

    It doesn’t; there’s no such thing as gamma-ray lenses and mirrors. There are two types of detectors on Fermi: 1) The Large Area Telescope (LAT), which converts an incoming gamma-ray into an electron-positron pair; various components of the detector allow us to reconstruct the direction and energy of the original gamma-ray. 2) The Gamma-Ray Burst Monitor, which uses a number of scintillators to detect gamma-ray bursts (funnily enough).

  28. IVAN3MAN

    JoeSmithCA:

    I wonder whats going inside a neutron star. What’s the material inside the star doing? Questions, questions, questions.

    Ask and you shall receive: Introduction To Neutron Stars

  29. IVAN3MAN

    Lab Lemming:

    How does a gamma ray telescope achieve focus?

    Ask and you shall receive: Coded Aperture Imaging High-Energy Astronomy

  30. IVAN3MAN

    DrFlimmer:

    Is it possible that a neutron star doesn’t collapse into a black hole due to its rotation? That he would be too massive to stay as a neutron star and only the centrifugal force keeps the neutron star alive? And with a little less angular momentum he would finally collapse?

    Neutron stars are very hot and are supported against further collapse because of the Pauli exclusion principle. This principle requires that no two neutrons can occupy the same quantum state simultaneously.*

    *Source: Wikipedia — Neutron Stars.

  31. TEO

    Who in their right mind needs religion when we got science? There are cool stuff in the real universe for us to discover everywhere.

    Science is COOL!

  32. TheWalruss

    Tod:
    And here I thought the high energy was coming from ultra-dense rotating stellar bodies…

  33. Just a quick pedantic note – there’s one other pulsar that I know of that’s not been observed to emit in radio. It PSRJ0537-6910 which has so far only been observed in X-rays. People have looked for radio pulses from it, but have not seen any yet. This pulsar is quite a bit further away than most though as it lives in the Large Magellanic Cloud at a distance of about 50 kiloparsecs. I think there might be some accreting millisecond pulsars that have generally only been observed at higher energies to, but I’m not sure about that.

  34. Annette

    @ TEO:

    “Science without religion is lame, religion without science is blind.”
    – Albert Einstein, “Science, Philosophy and Religion: a Symposium”, 1941

    Believe it or not, you can still have both. It doesn’t have to be black or white. ;) Now Einstein wasn’t known to be a religious man, but I think he said it well with that one quote. Thats why some of us are still in our right minds. :)

  35. Aodhhan

    Simple…

    Gravity is not constant, and this pulsar is able to hold everything back but gamma rays.
    There, I said it. Now let the ‘gasping’ begin!

  36. emf

    @Aodhhan: Yeah, I think you’re on to something there; although not the inconstancy of gravity. I would not be at all surprised to find that there was a relationship between the energy of the photons being emitted by a pulsar neutron star, and the physical size of that star in relation to it’s schwarzchild radius.

  37. Gary Ansorge

    I wonder if the neutronium formed by the gravitational collapse would remain neutronium if removed from that intense gravity filed, as in, held together by the strong nuclear force?

    If it could, would it be the stiffest material (theoretically) possible?

    If it could remain compacted, it would make one heck of an inertial energy storage device,,,with a compact core massing 100 kg, the core would be really small. Could drive my (electrically powered) Blazer 10,000 miles on a charge.

    Just looking for a SciFi story idea,,,

    Gary 7

  38. DrFlimmer

    Well, Ivan, I knew that, but thanks ;)

    I was just wondering, if there could be a neutron star who is too massive to be stable (so the Pauli principle cannot achieve enaugh pressure against gravitation) but gains is stability through its rotation.

    Anne, I think, too, that it would be quite unstable. But in theory such a neutron star could be out there – and if only for a short time…. ah, neutron stars, wounderful weired objects ;)

  39. Gary Ansorge

    Dang! Supposed to be “gravity FIELD”,,,

    (grabs coffee and ingests large quantity)

    GAry 7

  40. IVAN3MAN

    You’re welcome, DrFlimmer, I was just checking. :-)

  41. Jose

    @Aodhhan
    Gravity is not constant, and this pulsar is able to hold everything back but gamma rays.
    Gamma rays may have more energy than the rest of the electromagnetic spectrum, but gravity affects them the same way.

  42. gopher65

    That’s awesome!

    I suspect that the answer will turn out to be something like what Rob Keown suggested: the gamma ray beam is slightly wider than the radio beam, and we’re juuuuuust catching the edge of the beam.

    But any way you fry this, it is still cool.

  43. kappapavonis

    “If it doesn’t have quite that much oomph (if it has about 1 – 2.8 times the mass of the Sun) it forms a weird object called a neutron star”.

    ….. I thought neutron stars had to have a minimum mass above the Chandrasekhar Limit of 1.44 solar masses. Or have I got something wrong?

  44. Ryan

    @Aodhhan

    To expand on Jose, no. All light, from radio to gamma travels at the same speed. A black hole will trap all light, a neutron star will trap no light. I’m not positive, but it may be possible to have a gravitationally caused red shift. In that case you’d have the opposite: no gamma rays visible on the outside.

  45. Tom Marking

    “If it doesn’t have quite that much oomph (if it has about 1 – 2.8 times the mass of the Sun) it forms a weird object called a neutron star.”

    Since no one has caught this one, I thought I might mention it. I thought there was a minimum limit on the mass of a neutron star of 1.4 solar masses, not 1 solar mass. It’s called the Chandrasekhar limit. If the mass is below 1.4 solar masses then the object is supported by electron degeneracy pressure and becomes a white dwarf, not a neutron star.

  46. Tom Marking

    @DrFlimmer: “Is it possible that a neutron star doesn’t collapse into a black hole due to its rotation? That he would be too massive to stay as a neutron star and only the centrifugal force keeps the neutron star alive? And with a little less angular momentum he would finally collapse?”

    I’m not sure about neutron stars but this has definitely been observed with white dwarfs that rotate – they can be over the Chandrasekhar limit of 1.4 solar masses.

    http://en.wikipedia.org/wiki/Champagne_Supernova_(astronomy)

    “However, the progenitor of SN 2003fg reached two solar masses before exploding, more massive than thought possible. The primary mechanism invoked to explain how a white dwarf can exceed the Chandrasekhar mass is unusually rapid rotation; the added support effectively increases the critical mass. An alternative explanation is that the explosion resulted from the merger of two white dwarfs.”

  47. Tom Marking

    @Ian “I’m curious whether anyone has calculated what the rotational period of the sun would be if it were compressed to the size of a neutron star and retained its angular momentum”

    It’s a pretty simple calculation really.

    L = I * omega = I * (2*pi / T)

    where
    L is the angular momentum in kilogram – meter^2 per second
    I is the moment of inertia in kilogram – meter^2
    omega is the angular velocity in radians per second
    T is the period in seconds

    For a sphere of uniform density:

    I = 0.4 * M * R^2

    where
    M is the mass in kilograms
    R is the radius in meters

    So combining equations we have:

    L = 0.8 * pi * M * R^2 / T

    For the sun:
    M = 1.99E30 kilograms
    R = 6.96E8 meters
    T = 25 days = 2.16E6 seconds
    L = 1.12E42 kilogram – meter^2 per second

    The important point to remember is that L is conserved whether the sun contracts or expands so we have:

    T = 0.8 * pi * M * R^2 / L

    If the sun were to shrink to the size of a neutron star (i.e., radius = 12 kilometers) then it’s rotation period would be:

    T = 6.43E-4 seconds

    So it would rotate 1,555 times per second which is somewhat higher but still comparable to the fastest pulsars that have been measured.

    Hope this helps.

  48. DrFlimmer

    @ kappapavonis and Tom Marking

    You are both right that there is that threshold of 1.4 solar masses. But it doesn’t apply to neutron stars because there is a BIG difference in the formation process between a neutron star and a white dwarf which is limited by the Chandrasekhar limit.
    Also during a type-B-Supernova (or core-collapse-supernova as those guys are called, too, when neutron stars or black holes form) things are really weired, so there is no need for a neutron star to be “so massive”.

    If a core of a star burns out of fuel, that is it burns silicium to iron (not to mention that this process only takes few days – very short time!!), then iron-core finally collapses in a very short amount of time (some milli-seconds). The pressure is so high that the electrons are pressed into the protons to form a neutron and send out a neutrino. Although neutrinos do not interact very willingly with matter the density of the surrounding material is high enaugh that the cross section of neutrino-partical-interaction is rather big. So the neutrinos crash into the surrounding material and blow it off – the supernova explodes and leaves behind the degenerated core containing only neutrons.
    But the degeneracy depends on neutrons and not on electrons which means that we have another upper mass limit, but not a lower limit. A neutron star can actually be lighter than 1.4 solar masses due to the different formation processes.

    The Chandrasekhar limit is for electron degeneracy which does not apply for neutron stars but for white dwarfs. Those guys form rather non-violent compared to a supernova. If a light-weight star (like the sun) runs out of fuel the core contracts (very slowly ;) ) and settles finally when the electrons degenerate. The outer layers of the star have been shed throughout the lifetime of the star leaving behind the core.

    I hope I got these things right ;) I didn’t looked it up, but this is what I remembered.

    I still think it is amazing. Gravitation is always known to be “weak”, the weakest force at all. But finally it can overcome everything else if you don’t pay attention ;)

  49. Ian

    Thanks Tom, although I think I wasn’t clear enough. The problem I ran into when I tried it was that the sun’s rotation isn’t homogeneous; its period varies from 25-35 days depending on latitude, and it also appears to rotate faster at the core than at the surface (source: Wikipedia). That complicates the angular momentum calculation. Your estimate is probably correct to within an order of magnitude, though, and I guess I’ll have to be satisfied with that.

  50. Tom Marking

    “But why does it only emit gamma rays? Hey, good question. I don’t know the answer (and the press release doesn’t say, in fact). I suspect the answer right now is, we don’t know.”

    Isn’t the radiation from pulsars synchrotron radiation caused by charged particles rotating around magnetic fields. The frequency of emission is:

    Freq = B * q / (2 * pi * m)

    B is the magnetic field strength in teslas
    q is the charge of the particle in coulombs
    m is the mass of the particle in kilograms

    So for very high frequency radiation such as gamma rays the magnetic field is intense. The region where B is very large is close to the magnetic poles of the pulsar. X-rays will be generated farther out. Ultraviolet radiation still farther out, visible light even farther, and so on. Now, because the magnetic field lines curve around the geometry may be such that the gamma ray emitting region is aligned with our line of sight but the visible light emitting region is not.

    Or another alternative is that the gamma ray emitting region has lots of charged particles which allow it to emit strongly whereas the visible light emitting region is relatively depleted in charged particles. So there are lots of explanations that could explain the data. Finding out which explanation is correct is, of course, more tricky.

  51. Tom Marking

    @Ian “That complicates the angular momentum calculation.”

    Yes, it does. If you intend to correctly model pulsar formation you will need a supercomputer, and even then, you are likely to be wrong because we don’t have a good model. For example, the EOS (Equation Of State) for neutron stars which links temperature, density, pressure, etc. together is pretty much not known to any high degree of accuracy. Also, angular momentum is not conserved since mass is ejected from the star during the supernova event.

  52. IVAN3MAN

    @ DrFlimmer

    I’ve being doing some more checking and, yes, you’re right, but you have misspelled a couple of words more than once in your posts: it should be weird, not “weired”, and it should be enough, not “enaugh.” :)

    Excuse me for being a nitpicker, but I used to be a proofreader — old habits die hard!

    The “upper mass limit” that you mentioned, this is known as the Tolman-Oppenheimer-Volkoff (TOV) limit; there is some speculation that a quark star might be created if it has a density of between 2 to 3 solar masses, but any star of over 5 solar masses will inevitably collapse due to gravitational forces forming a black hole.

  53. @DrFlimmer “The Chandrasekhar limit is for electron degeneracy which does not apply for neutron stars but for white dwarfs.”

    If anyone knows, are there any known cases of binary pulsars where the combined mass of the two pulsars is less than 2.8 solar masses? Also, what would determine the lower limit for the mass of a neutron star? Could you have one with the mass of the earth or smaller?

  54. DrFlimmer

    @ Ivan

    Thanks a lot! My english is improving but there are still many errors – so correction always helps. And “enaugh” is a word I’m spelling wrong many times, I don’t know why…..

    @ Tom Marking

    I have no “real” answer for you, but I think that most neutron stars have masses of about 2 solar masses or more. I don’t know if it’s impossible to have a neutron star lighter than the earth, but I think this is VERY unlikely.

  55. Shane

    If we’re finding objects like this, imagine what else is out there!! We have found more different things in space that i can imagine…. alot of which tends to be VERY far away.. and that just happens to be things in the fraction of a percentage of space that we’re looking at… imagine all the stuff that is still out there, but we just haven’t happened to come across yet… this is amazing. i wish i were still alive a few thousand years from now when technology has increased to the point that we can experience these anomalies in a whole new way… mabye orbiting just outside of reach…

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