Smallest Known Black Hole Found

Here [arxiv.org] 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 [nasa.gov] 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.

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/tyXUTJza2Wc/smallest-known-black-hole-found

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