Supermassive Black Holes To Stars - It Wasn't Us!
A team of Yale University astronomers say that galaxies stop
forming stars long before their central supermassive black holes
reach their most powerful stage, meaning the black holes can’t
be responsible for shutting down star formation.
Astronomers believe that active galactic nuclei (AGN), the
supermassive, extremely energetic black holes at the centers of
many young galaxies, were responsible for shutting down star
formation in their host galaxies once they grew large enough. It
was thought that AGN feed on the surrounding galactic material,
producing enormous amounts of energy (expelled in the form of
light) and heat the surrounding material so that it can no
longer cool and condense into stars.
But the new research says that this shutting-down process
appears to take place much earlier in the AGN’s lifetime, well
before it starts shining brightly. “This high-luminosity phase,
when the AGN are at their biggest and brightest and most
powerful, is not the phase responsible for the shutdown of star
formation,” said Kevin Schawinski, a postdoctoral associate in
Yale’s astronomy department and lead author of the study in Astrophysical
The researchers analyzed images of 177 galaxies taken by two
different space telescopes to create a comprehensive view of
galaxies with AGN, including ones where the AGN were both
obscured by the galaxy’s dust and gas, and ones where there was
an unobstructed view of the AGN from the Earth’s vantage point.
Until now, some astronomers believed they can’t see AGN in any
galaxies that are still actively forming stars simply because
the light from the AGN is obscured by the galaxy’s gas and dust.
Schawinski and his team are the first to show that in fact there
are no bright AGN at the centers of star-forming galaxies.
By subtracting out the light from the AGN, the team discovered
that all of the galaxies with bright AGN had stopped forming
stars several hundred million years earlier. “The key result is
the finding that there is a lack of AGN in galaxies that are
currently forming stars,” said Meg
Urry, head of the Yale team and director of the Yale Center
for Astronomy and Astrophysics. “That tells us the AGN doesn’t
turn on until long after the stars stop forming.”
“For the first time, we’ve measured a real delay between the
end of star formation and the onset of a luminous AGN,” said
Schawinski. As for the real culprit, responsible for shutting
down star formation, “it’s possible that an earlier,
low-luminosity phase is responsible,” he said. “Either way, this
result shows that our previous understanding of how the
shutting-down process works wasn’t as simple as we thought.”
Article: Kevin Schawinski, Shanil Virani, Brooke Simmons, C.
Megan Urry, Ezequiel Treister, Sugata Kaviraj, and Bronika
Kushkuley, 'DO MODERATE-LUMINOSITY ACTIVE GALACTIC NUCLEI
SUPPRESS STAR FORMATION?', 2009 ApJ 692 L19-L23 doi: 10.1088/0004-637X/692/1/L19
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