NASA Announces Discovery of 30-Year-Old Black Hole 195
broknstrngz tips news of an announcement today from NASA about the discovery of a black hole in the M100 galaxy, roughly 50 million light-years from Earth. The discovery is notable because, if confirmed, it's now the youngest known black hole, born from the remains of a supernova we observed in 1979. Bad Astronomer Phil Plait explains why scientists think it collapsed to a black hole, rather than a neutron star: "The way a neutron star emits X-rays is different than that of a black hole. As a neutron star cools, the X-ray emission will fade. However, a black hole blasts out X-rays as material falls in; that stuff forms a flat disk, called an accretion disk, around the black hole. As this matter falls onto the newly created black hole, it gets heated to unimaginable temperatures — millions of degrees — and blasts out X-rays. In that case, the X-rays emitted would be steady over time. What astronomers have found is that the X-rays from SN1979c have been steady in brightness over observations from 1995 – 2007. This is very strong evidence that the star’s core did indeed collapse into a black hole." He also warns that we're not certain quite yet, and we'll have to keep our eye on it to make sure it's not a pulsar.
Because everyone else will say it too... (Score:1, Informative)
Don't you mean this instead? (Score:3, Informative)
He also warns that... we're not certain... quite yet, and... we'll have to keep... our eye on it to... make sure it's not a... pulsar.
Re:Because everyone else will say it too... (Score:5, Informative)
From our point in space, it is 30 years old.
But, more to the point, what we're observing now is a 30-year-old black hole. It's just that over where the black hole is, it's no longer 30 years old. That's not particularly relevant to us on Earth.
Re:"Keeping an eye on it" (Score:3, Informative)
If it's a pulsar, it's a neutron star; degenerate matter, but matter still, and not a black hole.
Relate to this! (Score:3, Informative)
Re:Relativity of Simultaneity (Score:4, Informative)
To all the inevitable pedantic responses about it not "really" happening 30 years old, I'll be even more pedantic. :) Relativity of Simultaneity, look it up. It's absolutely meaningless to talk of the temporal ordering of space-like separated events. In some suitable reference frame, it "really" did happen 30 years ago.
You've got that somewhat garbled. The relevant events would be (A) a photon is emitted from the star, and (B) that photon arrives here on earth. The relationship between A and B is lightlike, not spacelike. Since they are lightlike relative to one another, they do have a well-defined temporal ordering; there is no frame of reference in which B preceded A, or in which A and B are simultaneous. Your final sentence, however, is correct.
Re:Bad Astronomy? (Score:4, Informative)
It is correct to say that an accretion disk can form around a neutron star as well.
The distinguishing characteristic is that a neutron star bigger than its Schwarzschild radius. Not just a little bit bigger, but at least 11% bigger [see the Buchdahl-Bondi limit; this a theoretical limit for any perfect fluid spheres -- actual neutron stars don't come close to saturating that bound]. This means that the accretion of charged particles that is spiraling inward will eventually hit the surface, stopping the charged particles very rapidly. The radiation from suddenly stopping charged particles (Bremsstrahlung) is fairly distinctive, and is not seen here.
By contrast, an accretion disk around a black hole loses energy and eventually passes through the horizon. There is no sudden breaking and hence no Bremsstrahlung radiation It is the accretion disk and the lack of Bremsstrahlung that convinces us that the most likely candidate is a black hole.
[The reason the size limit was important is that as you get close to the horizon, redshifting makes things harder to see anyway. The point of the Buchdahl-Bondi theorem is that any perfect fluid sphere has to be about 11% bigger than the size of a black hole of equivalent mass. This limits the total redshift due to the object to a modest factor of 2, ensuring for a large class of matter (including neutron stars and all known matter to date) that the collision with the surface if it existed would be visible. This does not prevent unknown matter with exotic properties having s surface that is beyond the event horizon but close enough in the we would not see the Bremsstrahlung radition, but it is very difficult to construct "reasonable" solutions.]
Re:Because everyone else will say it too... (Score:3, Informative)
But then what happens when the black hole evaporates through hawking radiation and the event horizon disappears?
That will only happen after the black hole has fully formed and matter has stopped falling into it. Which, in our reference frame, is never. It only ever evaporates in local time.
Re:Because everyone else will say it too... (Score:3, Informative)
But then what happens when the black hole evaporates through hawking radiation and the event horizon disappears?
That will only happen after the black hole has fully formed and matter has stopped falling into it. Which, in our reference frame, is never. It only ever evaporates in local time.
The physics of cosmological singularities: breaking your brain since 1915.