Releases from NASA, NASA Galex, NASA's Goddard Space Flight Center, HubbleSite, Hinode, Spitzer, Cassini, ESO, ESA, Chandra, HiRISE, Royal Astronomical Society, NRAO, Astronomy Picture of the Day, Harvard-Smithsonian Center For Astrophysics, Max Planck Institute for Astrophysics, Gemini Observatory, Subaru Telescope, W. M. Keck Observatory, Fermi Gamma-ray Space Telescope, JPL-Caltech, etc
This composite image shows powerful radio jets from the supermassive
black hole at the center of a galaxy in the Phoenix Cluster inflating
huge "bubbles" in the hot, ionized gas surrounding the galaxy. The
cavities inside the blue region were imaged by NASA's Chandra X-ray
observatory. Hugging the outside of these bubbles, ALMA discovered an
unexpected trove of cold gas, the fuel for star formation (red). The
background image is from the Hubble Space Telescope. Image: ALMA (ESO/NAOJ/NRAO) H.Russell, et al.; NASA/ESA Hubble; NASA/CXC/MIT/M.McDonald et al.; B. Saxton (NRAO/AUI/NSF)
Astronomers observe black hole producing cold, star-making fuel from hot plasma jets and bubbles.
Phoenix cluster is an enormous accumulation of about 1,000 galaxies,
located 5.7 billion light years from Earth. At its center lies a massive
galaxy, which appears to be spitting out stars at a rate of about 1,000
per year. Most other galaxies in the universe are far less productive,
squeaking out just a few stars each year, and scientists have wondered
what has fueled the Phoenix cluster’s extreme stellar output.
Now scientists from MIT, the University of Cambridge, and elsewhere may have an answer. In a paper published today in the Astrophysical Journal,
the team reports observing jets of hot, 10-million-degree gas blasting
out from the central galaxy’s black hole and blowing large bubbles out
into the surrounding plasma.
These jets normally act to quench star formation by blowing away cold
gas — the main fuel that a galaxy consumes to generate stars. However,
the researchers found that the hot jets and bubbles emanating from the
center of the Phoenix cluster may also have the opposite effect of
producing cold gas, that in turn rains back onto the galaxy, fueling
further starbursts. This suggests that the black hole has found a way to
recycle some of its hot gas as cold, star-making fuel.
“We have thought the role of black hole jets and bubbles was to
regulate star formation and to keep cooling from happening,” says
Michael McDonald, assistant professor of physics in MIT’s Kavli
Institute for Astrophysics and Space Research. “We kind of thought they
were one-trick ponies, but now we see they can actually help cooling,
and it’s not such a cut-and-dried picture.”
The new findings help to explain the Phoenix cluster’s exceptional
star-producing power. They may also provide new insight into how
supermassive black holes and their host galaxies mutually grow and
McDonald’s co-authors include lead author Helen Russell, an
astronomer at Cambridge University; and others from the University of
Waterloo, the Harvard-Smithsonian Center for Astrophysics, the
University of Illinois, and elsewhere.
Hot jets, cold filaments
The team analyzed observations of the Phoenix cluster gathered by the
Atacama Large Millimeter Array (ALMA), a collection of 66 large radio
telescopes spread over the desert of northern Chile. In 2015, the group
obtained permission to direct the telescopes at the Phoenix cluster to
measure its radio emissions and to detect and map signs of cold gas.
The researchers looked through the data for signals of carbon
monoxide, a gas that is present wherever there is cold hydrogen gas.
They then converted the carbon monoxide emissions to hydrogen gas, to
generate a map of cold gas near the center of the Phoenix cluster. The
resulting picture was a puzzling surprise.
“You would expect to see a knot of cold gas at the center, where star
formation happens,” McDonald says. “But we saw these giant filaments of
cold gas that extend 20,000 light years from the central black hole,
beyond the central galaxy itself. It’s kind of beautiful to see.”
The team had previously used NASA’s Chandra X-Ray Observatory to map
the cluster’s hot gas. These observations produced a picture in which
powerful jets flew out from the black hole at close to the speed of
light. Further out, the researchers saw that the jets inflated giant
bubbles in the hot gas.
When the team superimposed its picture of the Phoenix cluster’s cold
gas onto the map of hot gas, they found a “perfect spatial
correspondence”: The long filaments of frigid, 10-kelvins gas appeared
to be draped over the bubbles of hot gas.
“This may be the best picture we have of black holes influencing the cold gas,” McDonald says.
Feeding the black hole
What the researchers believe to be happening is that, as jet inflate
bubbles of hot, 10-million-degree gas near the black hole, they drag
behind them a wake of slightly cooler, 1-million-degree gas. The bubbles
eventually detach from the jets and float further out into the galaxy
cluster, where each bubble’s trail of gas cools, forming long filaments
of extremely cold gas that condense and rain back onto the black hole as
fuel for star formation.
“It’s a very new idea that the bubbles and jets can actually influence the distribution of cold gas in any way,” McDonald says.
Scientists have estimated that there is enough cold gas near the
center of the Phoenix cluster to keep producing stars at a high rate for
another 30 to 40 million years. Now that the researchers have
identified a new feedback mechanism that may supply the black hole with
even more cold gas, the cluster’s stellar output may continue for much
“As long as there’s cold gas feeding it, the black hole will keep
burping out these jets,” McDonald says. “But now we’ve found that these
jets are making more food, or cold gas. So you’re in this cycle that, in
theory, could go on for a very long time.”
He suspects the reason the black hole is able to generate fuel for
itself might have something to do with its size. If the black hole is
relatively small, it may produce jets that are too weak to completely
blast cold gas away from the cluster.
“Right now [the black hole] may be pretty small, and it’d be like
putting a civilian in the ring with Mike Tyson,” McDonald says. “It’s
just not up to the task of blowing this cold gas far enough away that it
would never come back.”
The team is hoping to determine the mass of the black hole, as well
as identify other, similarly extreme starmakers in the universe.