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Fraser
2006-Jan-07, 01:04 AM
SUMMARY: Astronomers have found evidence of monstrous black holes at the heart of galaxies with the mass of millions of stars, or ones with just the mass of a single star. But not much in between (100 to 10,000 stellar masses). One of the newest pieces of evidence for a medium-sized black hole was captured by NASA's Chandra X-Ray Observatory. It measured the orbit of a star trapped in a death spiral around one of these medium-mass black holes.

View full article (http://www.universetoday.com/am/publish/nasa_doomed_blackhole.html)
What do you think about this story? post your comments below.

VanderL
2006-Jan-07, 10:24 AM
SUMMARY: Astronomers have found evidence of monstrous black holes at the heart of galaxies with the mass of millions of stars, or ones with just the mass of a single star. But not much in between (100 to 10,000 stellar masses). One of the newest pieces of evidence for a medium-sized black hole was captured by NASA's Chandra X-Ray Observatory. It measured the orbit of a star trapped in a death spiral around one of these medium-mass black holes.

View full article (http://www.universetoday.com/am/publish/nasa_doomed_blackhole.html)
What do you think about this story? post your comments below.

Did anybody check the images with this article?
Here (http://chandra.harvard.edu/photo/2000/m82bh/index.html) are the images I mean, plus the caption. I'm totally confused about the information, I can make out 4 objects (not 1) that have changed in brightness between the 2 snapshots, 2 of them brightening and 2 of them dimming. No mention of these objects in the caption. Does anybody know what is going on here, are they known variable stars?

Cheers.

01101001
2006-Jan-07, 12:04 PM
I'm totally confused about the information, I can make out 4 objects (not 1) that have changed in brightness between the 2 snapshots, 2 of them brightening and 2 of them dimming. No mention of these objects in the caption. Does anybody know what is going on here, are they known variable stars?

Not variable stars. These are X-ray images of the central part of the M82 galaxy, each approximately 2500 lightyears across. They are zoomed in from this wider Chandra X-ray image (http://chandra.harvard.edu/photo/2000/0094/).


The bright spots in the center of this Chandra X-ray image are supernova remnants and X-ray binaries. These are some of the brightest such objects known. The luminosity of the X-ray binaries suggests that most contain a black hole.

I suspect they are probably all active and vary over time. The discovery in the news was that one had a 62-day periodic component to it, indicative of a stellar companion.

ngold
2006-Jan-07, 03:09 PM
Separate thought:

Am I right, that by current theory, there are three varieties of black holes
-small, which came from the collapse of a single large mass star
-massive, which came from the collapse of clouds of gas, and
-medium, which we're not sure yet?

VanderL
2006-Jan-07, 03:29 PM
Not variable stars. These are X-ray images of the central part of the M82 galaxy, each approximately 2500 lightyears across. They are zoomed in from this wider Chandra X-ray image (http://chandra.harvard.edu/photo/2000/0094/).

I suspect they are probably all active and vary over time. The discovery in the news was that one had a 62-day periodic component to it, indicative of a stellar companion.

Thanks for trying to explain this to me, it seems that all the X-ray sources are variable (if I look at the image the variation is very large). All of them are thought to be powered by a black hole/neutron star, because all of them are very bright. Does the presence (or absence) of any periodicity tell us if the source has a companion? Does this mean that when there is no periodicity there is no companion star? How is the "normal" variation explained?

Cheers.

01101001
2006-Jan-08, 04:35 PM
Thanks for trying to explain this to me, it seems that all the X-ray sources are variable (if I look at the image the variation is very large). All of them are thought to be powered by a black hole/neutron star, because all of them are very bright. Does the presence (or absence) of any periodicity tell us if the source has a companion? Does this mean that when there is no periodicity there is no companion star? How is the "normal" variation explained?

Cheers.

Normal variation, non-periodic, irregular, appears to me to be the result of the random chance of the black hole gaining more matter while going about its business.

NASA: Imagine the Universe: Science: Black Holes (http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html)


Another sign of the presence of a black hole is random variation of emitted X-rays. The infalling matter that emits X-rays does not fall into the black hole at a steady rate, but rather more sporadically, which causes an observable variation in X-ray intensity.

I don't see how the lack of a periodic component would rule out a companion. The companion(s) might not be donating mass, or the peridoic component might be too small or too infrequent to measure among the noise.

John Dlugosz
2006-Jan-09, 04:23 PM
OK, how does the object's orbital period tell you about its density?