Expert: Jayendra Upadhye - 1/19/2005

Question
sir
 I am a student of Astronomy in osmania University in India . I want to know what is the employment after completion of my M.sc degree. Also i want list of reaserch institutions of Astronomy in abroad .Could you plese send me that details.

here my Qusetions is how the black holes are identified.  
       thanking you sir,  

Answer
Rajesh!
I am NOT a professional astronomer!
I did look up in Yahoo search engine using the string "jobs astronomy inda" and 134,000 pages!
On the first page itself i could see the following links!

1 - National Centre for Radio Astrophysics
[operates the giant metrewave radio telescope, near Pune, India.] http://rds.yahoo.com/S=2766679/K=job+astronomy+india/v=2/SID=e/TID=F344_70/l=WS1...

2 - Job Register - Detail Page
[positions in Astronomy and Astrophysics-RAMAN RESEARCH INSTITUTE, BANGALORE, INDIA ... Bangalore, India. The Raman Research Institute ... Faculty positions in Astronomy and Astrophysics. ]
http://rds.yahoo.com/S=2766679/K=job+astronomy+india/v=2/SID=e/TID=F344_70/l=WS1...

3 - Job Register - Detail Page  
[Post-doctoral positions in Astronomy and Astrophysics-INTER-UNIVERSITY CENTER FOR ASTRONOMY AND ASTROPHYSICS, PUNE, INDIA. No. 20208. Post-doctoral positions in Astronomy and Astrophysics]
http://rds.yahoo.com/S=2766679/K=job+astronomy+india/v=2/SID=e/TID=F344_70/l=WS1...

4 - Jodrell Bank - UK Online Banking Junction  
[Jodrell Bank - UK Online Banking Junction Online Bank providers and brokers. Great value uk Banks. ... daily bank hsbc india updates. ... jeff bank job in banking jodrell bank ... html. 125. ASTRONOMY WEBSITES - Planets, astronomy software, news, star charts, astronomy societies, facts ...]
http://rds.yahoo.com/S=2766679/K=job+astronomy+india/v=2/SID=e/TID=F344_70/l=WS1...

5 - Ask An Astronomer > Career and Courses  
[You should note that there is no manned space flight in India. Should there ever be one, it is likely that the first candidates would come from one of the Armed Services, perhaps the Air Force. ... to study Astronomy in India ? ... India offers Astronomy courses ? What courses should one pursue after twelfth standard for a career in Astronomy ? What are the ]
http://rds.yahoo.com/S=2766679/K=job+astronomy+india/v=2/SID=e/TID=F344_70/l=WS1...

Last of all, surf the web yourself to find a job that suits you!

Now to your question.
These can be identified [always indirectly], in two ways.

1 - [sample case Cygnus X-1 that had become quite famous in the late 70s. there had been articles in the times of india and i had even attended a talk by a scientist of the Space application center in Ahmedabad (or was it the Physical research laboratory?) on that subject.]
In this case, the black hole orbits a red giant star so closely, that its skims off its tenuous outer atmosphere into an accretion disk around itself. Near the event horizon, these gases emit hard x rays as they are squeezed to unbelievable extents. Detecting the x-rays but finding no visible orbiting companion to the red giant star, is a dead give away to the existence of a black hole.

2 - The other is when a star's spectrum shows a "wobble" (red and blue shift cycles as the star moves towards and away from us, in its orbit around the center of mass of the system). And we fail to find enough visible matter in the form of large planets or binary stellar companion. In such a case, the existence of a black hole in its close orbit is suspected.

Note:- Black holes are also associated with gravitational lensing, but so far no known holes associated with this phenomenon have been detected.

The hubble telescope has seen gravitational lensing when searching for quasars, where distant galaxies themselves act as huge gravitational lenses and show clear arcs of distorted images of even further galaxies, encircling their images, like broken rings!

refer:-
This hubble image clearly shows the Abell 2218 cluster of galaxies lensing the light of a quasar that is the farthest detected object by the hubble deep field so far. red shift 7.
link:
http://antwrp.gsfc.nasa.gov/apod/ap040217.html
Jayen