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Smallest Known Black Hole Found
smitty777 writes "Adding to the recent black hole discoveries of gas clouds and a quasar accretion disc, Forbes is reporting on a recent discovery by NASA's Rossi X-Ray Timing Explorer (RXTE) on the smallest known black hole. From the article: 'If the astronomers' calculations are correct, this black hole is located about 16,000 to 56,000 light years away from Earth (a more precise distance hasn't yet been determined). The black hole itself is only about three times the mass of the Sun, which means that the original star was just barely big enough to form a black hole.'"
WHAT THE FUCK! Is this for real? Maybe I'm just imagining this, but this article looks like, dare I say it, it may just be "news for nerds!" After months of articles about various shitty Apple devices, copyright, American politics, and shitty Apple devices again, it's stunning to finally see an article about a scientific discovery again.
That's a tight hole.
Fuck systemd. Fuck Redhat. Fuck Soylent, too. Wait, scratch the last one.
There have been a bunch of claims of black holes roughly in the range 3-4x solar masses, some subsequently revised upwards (this one made some news in 2008, and there are some other candidates as well). The "normal" range for stellar black holes is roughly 3-30x solar masses, according to current understanding.
Anyone have a link to a good explanation of the current estimated values for a minimum? My understanding is that there isn't really a theoretical physical minimum (black holes can exist at any size), but that there's a mass level beneath which astrophysicists consider it very unlikely that conditions would have really existed to produce a black hole through stellar collapse of a star. But I can't seem to find a solid estimate of what that number is, just these sorts of indirect references to 3x being "close" to the minimum (looking at Google Books, I find an old textbook that also mentions 3.2x as "just above" the theoretical minimum, but doesn't elaborate).
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
This is the probably the last big science release for Rossi X-ray Timing Explorer (RXTE). RXTE will be turned off at the end of this year and disabled. This is mostly because of NASA budget reductions and reduced prioritization by peer review committees, but also because of its aging on-board systems. The systems were designed for a two year life-time but lasted for more than sixteen! The satellite will probably remain in orbit for quite a few more years - passive - before re-entering the atmosphere. The scientific community will lose the only working X-ray observatory that can measure the fast heartbeats of black holes and neutron star systems, and do complicated monitoring observations.
RXTE has done a lot of great science in the past 16 years, some of it featured here on Slashdot. The legacy will live on though, since the data archive will remain publicly available. Sometimes great science can come from the archive as well!
(speaking for myself only) CM
A black hole that would grow by absorbing radiation instead of shrinking at the ~4K average temperature of the universe can be around the mass of the Moon. Such a small black hole cannot form just by gravitational collapse but can go on indefinitely unless the universe cools down.
The question here was about the minimum mass a star can have to become a black hole instead of remaining a neutron star - or maybe something more exotic but still fighting gravity. The Tolman–Oppenheimer–Volkoff equation gives an estimate but since noone managed to observe exactly what happens with matter at the densities found in a neutron star there are still a lot of assumptions.
Here is the scientific paper. It makes no claim whatsoever about the mass of IGR J17091-3624. On p. 6, they say:
Figure 5 implies that if IGR J17091-3624 emits at Eddington, then either it harbors the lowest mass black hole known today (< 3Msolar for distances lower than 17 kpc), or, it is very distant. Such a large distance, together with its b ~2.2deg Galactic latitude, would imply a significant, but not necessarily implausible, altitude above the disk
Here is the NASA press release summarizing the paper for people who aren't scientists. It quotes the lead author as saying:
Just as the heart rate of a mouse is faster than an elephant's, the heartbeat signals from these black holes scale according to their masses
The Forbes article morphs this into "NASA Satellite May Have Found The Smallest Known Black Hole," and says, "An international team of astronomers utilizing NASA's Rossi X-Ray Timing Explorer (RXTE), believe that they've identified a candidate for the smallest known black hole[...]"
The slashdot summary says:
The black hole itself is only about three times the mass of the Sun[...]
This is completely incorrect. It's a candidate for a very low mass black hole. What that means is that they're suggesting that astronomers do follow-up observations on this object and actually determine its mass, which may be unusually low.
It is of very great interest to relativists and astronomers to find the smallest black holes. There is a limit called the Tolman-Oppenheimer-Volkoff limit on the largest mass that a neutron star can have. There are big theoretical uncertainties in this number, but it is probably around three solar masses. However, we don't know for sure whether anything too massive to be a stable neutron star necessarily becomes a black hole. There have been all kinds of goofy objects hypothesized by theorists that might be intermediate between neutron stars and black holes, including black stars, gravastars, fuzzballs, quark stars, boson stars, and electroweak stars. Observing a low-mass black hole narrows the gap in mass between the heaviest stable neutron star and the lightest black hole, leaving less wiggle room to believe in these exotic objects.
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