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A black hole found inside a globular cluster! January 7, 2007

Posted by dorigo in astronomy, Blogroll, internet, news, physics, science.

Through The Arcadian Functor and Babe in the Universe (see links in the blogroll column) I learned that a team searching for black holes through rapidly varying x-ray signals has found a intermediate-size black hole inside a globular cluster in the halo of NGC4472, a not-too-conspicuous ellyptical galaxy in the Virgo cluster (also known as M49, see picture on the right).

By the way, I saw it through my dobson telescope last summer… It is a Mv=8.5 object, and I wonder how faint is the globular they found to contain the black hole.

Anyway. According to the researchers, they were prepared for a long search, but they “found one as soon as we started the search. It was only the second globular cluster we looked at.”

Besides the wonderful and intriguing implications of this observation – black holes are not expected in the core of globular clusters if you ask the experts, although I had always thought it was a pretty obvious guess that they must be there – there remains the excitations for the next bunch of data they will produce, and a question.

Indeed, the method they adopted to find black holes was to look for rapidly varying x-ray sources associated to visible light objects (the globulars) with a extremely high spatial resolution probe, the European Space Agency’s XMM-Newton satellite (see http://www.esa.int/esaCP/SEML0QZTIVE_index_0.html). But for sure they did not specifically aim at that globular cluster to see the x-ray signal! They have sensitivity to large areas of the sky. So the claim that the globular was “the second they looked at” is a lie deceiving.

What they probably did was to observe a source of x-rays, and then match it to a list of known objects lying close by. The second in the list probably matched spatially to the x-ray signal well enough to provide certainty of an identity between light and x-ray source.

I would be happy to be mistaken… Does anybody know more about this issue ?



1. Kea - January 17, 2007

Hi Tommaso. Great post! I’m sorry that I only spotted it now. Unfortunately, I don’t have a subscription to Nature (or anything else for that matter). Maybe we could email them? Google gave me some earlier links.

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