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Old 10-03-2012, 01:44 PM
Location: Wasilla, Alaska
17,825 posts, read 20,504,794 times
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Twin Black Holes Inside Globular Star Cluster Confound Astronomers

A pair of black holes found at the heart of a globular cluster is causing astronomers to rethink the idea that these dense bundles of stars should have only one black hole at their center.

Messier 22 (M22) is about 10,600 light-years away from Earth, and contains hundreds of thousands of stars tightly bound by gravity.

Using the Karl G. Jansky Very Large Array (VLA) in New Mexico, the astronomers studied M22 in search of an intermediate-mass black hole, which is smaller than the supermassive black holes found in galaxies’ centers, but larger than black holes that are several times the sun’s mass.

Instead, the team found two smaller black holes about 10 to 20 times heavier than the sun.

Source: Twin Black Holes Inside Globular Star Cluster Confound Astronomers | Space & Astronomy | Science | Epoch Times
The article could have been a little clearer. Intermediate-mass black holes are several THOUSAND times the sun's mass. Stellar-mass black holes must be at least 10 times the sun's mass.

Astronomers spot the very first intermediate-mass black hole

M22 also is very uncommon compared to other globular clusters. There is a planetary nebula located in M22.
  1. it is only 1 of 2 known in globular clusters,
  2. it is only 1 of 4 known to be completely devoid of hydrogen, and
  3. it is only 1 of about 3 known to be sweeping through the interstellar medium.
The star at the center of the planetary nebula is a blue star. The planetary nebula (designated GJJC1) is estimated to be a mere ~6,000 years old.

M22 has an estimated age of 12 billion years, which means that it formed about the same time as the Milky Way. It also means that there should be numerous stellar-mass black holes within M22. What makes M22 odd is what we are not finding. If M22 is as old as the Milky Way, why have the close proximity stellar-mass black holes not become incorporated into a single intermediate-mass black hole?

Planetary Nebula IRAS 18333-2357 in M22
Interpreting the M22 Spike Events - Abstract - The Astrophysical Journal - IOPscience
Initial conditions for globular clusters and assembly of the old globular cluster population of the Milky Way - Marks - 2010 - Monthly Notices of the Royal Astronomical Society - Wiley Online Library
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