Galaxy's quasar radiation cuts off star formation in its cosmic neighbour
Pune: What happens when two galaxies racing towards each other at 500km per second collide? For the first time, an international team of astronomers, including two from Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune, found that sometimes the core of one galaxy throws out so much radiation at the other galaxy that it loses its power to form stars.
Bright objects called quasars are the villains disrupting star formation. They are produced by the merger of galaxies and are powered by black holes found in the core of the galaxies.
By combining optical and millimetre-wave observations obtained with Very Large Telescope (VLT) and Atacama Large Millimetre/submillimeter Array (ALMA) telescopes in Chile, the team identified a galaxy interacting with another that hosts a quasar and found that radiation from the quasar altered the structure of the other galaxy's interstellar gas.
What was left behind was not enough to form stars. The paper was published in Nature on May 21.
IUCAA's director Raghunathan Srianand compared the phenomena to waking up a sleeping monster which will influence everything around it. "While it was predicted in theory, there was no direct evidence until now," he added.
Srianand explained that black holes are at the centres of all galaxies. "Like a hungry monster, black holes swallow everything that fall into them and emit radiation which is called a quasar.
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When the black hole doesn't have gases to feed on it becomes quiet. Because nothing is falling in, no radiation is emitted," he said.
Theoretical scientists believe that black holes are quiet because there is no gas around but they come alive when one or more galaxies collide with them. "Suppose there is a black hole in a galaxy. If another galaxy interacts with it, it can attract some gas from the second galaxy and become active because it has the fuel.
The theory that when two galaxies merge, the black hole in the centre will become bright was proposed a long time ago, this is the first time it was observed by us last year," said Srianand.
Srianand said if a black hole is quiet in a galaxy, the surrounding regions will behave differently compared to one radiating light. Scientists predicted that such radiation will destroy, evaporate, or heat the gas in the surrounding region where new generations of stars are formed.
Consequently, that region must wait until the gas around the black hole is completely consumed by it, and it becomes quiet once more.
"Essentially, we found two things: that when there is a merger, there will be a quasar. The second is that when there is a quasar, we can find how much material is present in the vicinity through calculations. It helps decide whether that much material is sufficient to form stars. In the present observation, we found that it is not sufficient to form stars."
A year of difficult calculations and analysis
An international team led by Sergei Balashev (Ioffe Institute, Saint Petersburg, Russia) and Pasquier Noterdaeme (Institut d'Astrophysique de Paris, France) that includes IUCAA researchers Neeraj Gupta and Raghunathan Srianand are behind this discovery
The team from IUCAA, France, Russia, and Chile has been working together for the last 20 years. The idea is to look into the faraway universe and detect molecules and other things
For example, light from this object would have taken about 10 billion light years to reach us.
If you take the universe's current age to be around 12 billion, it would have been two billion years then, Srianand said.
quote
We use a spectroscopic technique where one looks at emission, absorption lines, and radiation coming from various processes. This measurement is an extremely difficult one. It took us nearly a year to convince the community that what we are seeing is unique. What we observed has been confirmed through theoretical calculations as well as solid observational results
Raghunathan Srianand I IUCAA's director
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