Image: Starving black hole
An illustration of a black hole "starving" as its surrounding gas is evaporated.
updated 1/12/2009 8:04:42 PM ET 2009-01-13T01:04:42

Supermassive black holes are thought to lurk at the heart of essentially all galaxies bigger than our own. Their powerful gravity should be luring in galactic matter, feeding the black holes' voracious appetites.

However, while plenty of gas is available for these black holes to feast upon, few of them have been observed to actively accrete gas from their home galaxy, presenting astronomers with a puzzle as to why these black holes aren't eating. Something must be preventing the black holes from accreting gas, though no one has known exactly what that was.

"This has been a longstanding problem," said Q. Daniel Wang of the University of Massachusetts at Amherst.

Now, Wang and his colleagues have some possible suspects behind the starving black holes: exploding stars, or supernovas.

Wang and his team investigated the starvation of the supermassive black holes at the center of two galaxies, M31 (aka the Andromeda Galaxy, our nearest galactic neighbor) and NGC 5866. They presented their findings here this week at the 213th meeting of the American Astronomical Society.

With both of these galaxies, and others, the precise clue that the galaxies aren't feeding is the lack of large amounts of radiation coming from the nucleus of the galaxy, which astronomers would expect to detect from an actively eating black hole. What makes the lack of radiation most perplexing is that plenty of gas should be expelled by older stars and their remnants, such as planetary nebulas, and accumulating in the galactic bulges of the galaxies (the tightly-packed group of stars found in the center of galaxies, where the black hole resides).

What was happening to that gas has been a mystery. Astronomers had surmised that the gas "has to be removed continuously from the bulge," Wang said, otherwise the black holes would be feasting on it.

Some astronomers thought gravitational influences from nearby galaxies could be sucking away the gas. But Wang's study suggests it's actually an internal problem generated by powerful supernova explosions.

These explosions occur when a massive star's core stops generating energy and collapses in on itself, releasing energy that heats and expels the star's outer layers — the star goes supernova.

Supernovas come in slightly varying types.

Type 1a supernovas are constantly exploding throughout a given galaxy. These exploding stars send out a shockwave — what Wang calls an "interstellar tsunami" — that propagates throughout the gas in the galaxy. Wang and his team simulated the effect of these shockwaves on the gas accumulation around the galaxy's center.

The interstellar tsunami works in a similar manner to tsunamis on Earth: The shockwave generated by an earthquake below the ocean has little effect where the ocean is deep and can absorb the energy, but when that wave reaches shallow water, it forms the characteristic enormous wave that slams onto the coast.

Likewise, the hot gas in the galaxy can absorb the supernova's shock, but when the wave reaches the cool gas expelled by dying stars, it steepens and pounds the central disk of the galaxy, evaporating the gas.

Because these supernova explosions are happening all the time, they continue to pound away at the disk; the gravity of a less massive galaxy can't counteract the evaporating energy of the supernovae, so the gas can't accumulate, and the black hole starves.

The interruption of the gas accumulation also affects the evolution of the galaxy, Wang noted.

More massive galaxies, on the other hand, have a bigger gravitational pull that keeps the gas from leaving.

"It's a much more difficult escape," Wang told "Eventually gravity wins."

© 2013 All rights reserved. More from

Photos: Month in Space: January 2014

loading photos...
  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
  1. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  2. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  3. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.

  4. Editor's note:
    This image contains graphic content that some viewers may find disturbing.

    Click to view the image, or use the buttons above to navigate away.


Discussion comments


Most active discussions

  1. votes comments
  2. votes comments
  3. votes comments
  4. votes comments