Supermassive black holes could leave behind long-lasting infrared afterglows visible to current instruments when they merge, a new study says. If so, scientists could find signs of these mergers much sooner than expected.
Supermassive black holes weigh millions or billions of times the mass of the Sun and appear to reside in the hearts of most galaxies the size of the Milky Way or larger.
Their mergers are predicted to be among the most powerful events in the universe, with each union generating more energy than all the stars in the cosmos combined.
Most of that energy is thought to be released in the form of gravitational waves
- elusive ripples in the fabric of space that have yet to be directly detected.
Crashing particles
But new calculations by Jeremy Schnittman and Julian Krolik at Johns Hopkins University in Maryland, US, suggest that recently merged black holes give off an infrared glow for up to 100,000 years.
The persistent auras originate from the thick clouds of gas and dust, called accretion discs, which surround and sustain the black holes.
According to the calculations, when two black holes collide, the orbits of material in the disks become disturbed, causing particles to crash into one another.
"It takes a while for the gas to settle down into a new circular orbit, and as it sloshes around, it loses a lot of energy by smashing into itself," Schnittman told New Scientist.
Some of that energy is transformed into X-rays and other forms of light, which bounce around in a labyrinth of gas and dust particles in the accretion discs before ultimately escaping in the form of infrared light.
Infrared only
The resulting infrared glow from some of these events could be visible to NASA's infrared Spitzer Space Telescope, the researchers say.
And unlike other infrared sources in the sky, newly merged black holes should not emit X-rays or ultraviolet light. "We want to find something that has infrared and nothing else," Schnittman said.
Kristen Menou, an astrophysicist at Columbia University in New York who was not involved in the study, said the idea is a "very interesting proposal in that it can be falsifiable with current facilities."
Schnittman and Krolik estimate that 100,000 infrared sources from merged supermassive black holes could be visible in the universe today. They have submitted their research to the Astrophysical Journal.
The gravitational waves given off by supermassive black hole mergers could also be detected one day. But the frequency of these waves is too low to be picked up by current gravitational wave detectors like LIGO (Laser Interferometer Gravitational Wave Observatory).
A proposed space mission called LISA (Laser Interferometer Space Antenna) should be able to see them, but it is not expected to launch until 2018.
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Have your say
Who's Doing The Math?
Tue Mar 04 21:27:15 GMT 2008 by Cyrus
Given that the <i>only</i> supermassive blackholes postulated to exist in the universe, are <i>only</i> to be found at the centers of galaxies at least as big as the milky way; and given that the infrared glow lasts for a mere 100,000 years, it is quite ludicrous to suggest that there are 100,000 of these objects currently visible in the universe. Just how many very large galaxies do the authors believe collide in 100,000 years?
Who's Doing The Math?
Wed Mar 05 01:44:37 GMT 2008 by Charles
Isn't the number of galaxies in the visible universe of the order of 10^10? If so, for there to be 10^5 of these things visible, would that mean one a collision per year? Or would it? Anyway, someone with a more mathematical background can surely work it out quite easily!
PS - note to the editor - disc is spelled "disc" outside the US.
Who's Doing The Math?
Wed Mar 05 01:54:34 GMT 2008 by Shmulik
As Charles points out, there are roughly 10^10 super-massive black holes in the observable universe. If each one merges only ONCE in the entire lifetime of the universe (10^10 yrs) then there should be 1 merger per year, or 10^5 at any one time if each afterglow lasts 10^5 years. Pretty simple math, Cyrus.
Who's Doing The Math?
Thu Mar 06 22:46:42 GMT 2008 by Cyrus
I think it's time you pulled your heads out of your math-holes.
First of all, there are 10^10 galaxies in the visible universe, not 10^10 super-massive black holes, as only those galaxies at least as big as the Milky Way are supposed to contain them (assuming they exist at all). Second, the interaction of galaxies do not follow gas laws. Perhaps you haven't been paying attention, but it now known that the universe's galactic superclusters are accelerating away from from each other, whilst the galactic superclusters themselves are, generally speaking, static. Estimating that there is 1 collision annually is ludicrous. If, in the future life of the universe, a single collision of super-massive black holes occured, it would be nothing short of a miracle. Third, maybe you didn't notice, but each super-massive black hole is surrounded by an enormous galaxy of around 10^10 stars. Does anyone really believe that you will see this infrared afterglow through the infrared light given off by all these stars? We can't even see the center of our own galaxy! Finally, if such a collision were to give off more energy than produced by all the visible stars in the observable universe in an instant, as postulated, do you really think any intelligent beings would be left in the universe to view the afterglow?
Wake up people.
Who's Doing The Math?
Fri Mar 07 15:06:02 GMT 2008 by Shmulik
Wow, Cyrus, your rudeness is matched only by your impressive ignorance (but isn't that so often the case?).
As a matter of fact,
YES, all those galaxies are expected to host black holes.
YES, those galaxies and their central black holes collide all the time, especially those in clusters, which are anything but static.
YES, we can easily see the black holes, which in many galaxies are far brighter than all the stars combined (our sun gives off 10^33 ergs/sec, but a quasar shines at 10^46 ergs/sec or more!)
and NO, the energy from such a collision would not kill us all because it is in the form of gravitational waves, which couple only very weakly to matter--that's why they are so hard to see in the first place!
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