Could Supermassive Black Holes Explain Our Universe's Gravitational-Wave 'Hum'? (space.com) 19
"Earlier this year, after 15 years of searching, scientists finally heard the background hum of low-frequency gravitational waves that fill our universe," writes Space.com.
"Now, the hard work of searching for the source of these ripples in spacetime can begin." Currently, the primary suspects in this case are pairings of supermassive black holes with masses millions, or even billions, of times that of the sun. However, that doesn't mean that there isn't room for a few unusual suspects, which could potentially point us toward new physics....
[G]ravitational waves detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) express wavelengths that are thousands of miles (or km) in length and hold frequencies of milliseconds to seconds. The new gravitational waves detected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), by contrast, have wavelengths on a scale of trillions of miles (or km). This is similar to the distance between the sun and its neighboring star, Proxima Centauri, a staggering 20 light-years in length. Plus, NANOGrav gravitational wavelengths have frequencies on scales of years instead of mere seconds. Practically, what this means is scientists need to build over 15 years of NANOGrav data to confirm a low-frequency gravitational wave detection.
But, when it happens, it's worth the wait. That's because these results have the capacity to point us toward new information about our universe... "The detection of low-frequency gravitational waves means they're from very different sources to the LIGO and Virgo sources, which are stellar mass black holes and neutron star mergers," Scott Ransom, a National Radio Astronomy Observatory astronomer and former chair of NANOGrav, told Space.com... Ransom is part of a collaboration of researchers that believe low-frequency gravitational waves, including those detected by NANOGrav, may originate from a pretty incredible source. They could come from, the team argues, hundreds of thousands of supermassive black hole pairings that, over the 13.8-billion-year course of cosmic history, came close enough together that they've merged...
"For many decades, theorists have hypothesized that supermassive black hole binaries should produce a signal with characteristics just like what NANOGrav and other pulsar timing arrays are seeing," Luke Zoltan Kelly, a Northwestern University theoretical astrophysicist and NANOGrav researcher, told Space.com. "For most of the community, supermassive black hole binaries are a natural best guess for what's producing the gravitational wave background...." Zoltan Kelley pointed out to Space.com that besides binaries, there are a number of new models in cosmology and in particle physics that, under the right circumstances, could also produce a similar gravitational wave background to that detected by NANOGrav. For example, axion or 'fuzzy' dark matter, cosmic strings, inflationary phase transitions, and many others," the Northwestern astrophysicist said.
"What's really exciting about these possibilities is that each of these models is an attempt to explain some of the biggest current mysteries of our universe."
"Now, the hard work of searching for the source of these ripples in spacetime can begin." Currently, the primary suspects in this case are pairings of supermassive black holes with masses millions, or even billions, of times that of the sun. However, that doesn't mean that there isn't room for a few unusual suspects, which could potentially point us toward new physics....
[G]ravitational waves detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) express wavelengths that are thousands of miles (or km) in length and hold frequencies of milliseconds to seconds. The new gravitational waves detected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), by contrast, have wavelengths on a scale of trillions of miles (or km). This is similar to the distance between the sun and its neighboring star, Proxima Centauri, a staggering 20 light-years in length. Plus, NANOGrav gravitational wavelengths have frequencies on scales of years instead of mere seconds. Practically, what this means is scientists need to build over 15 years of NANOGrav data to confirm a low-frequency gravitational wave detection.
But, when it happens, it's worth the wait. That's because these results have the capacity to point us toward new information about our universe... "The detection of low-frequency gravitational waves means they're from very different sources to the LIGO and Virgo sources, which are stellar mass black holes and neutron star mergers," Scott Ransom, a National Radio Astronomy Observatory astronomer and former chair of NANOGrav, told Space.com... Ransom is part of a collaboration of researchers that believe low-frequency gravitational waves, including those detected by NANOGrav, may originate from a pretty incredible source. They could come from, the team argues, hundreds of thousands of supermassive black hole pairings that, over the 13.8-billion-year course of cosmic history, came close enough together that they've merged...
"For many decades, theorists have hypothesized that supermassive black hole binaries should produce a signal with characteristics just like what NANOGrav and other pulsar timing arrays are seeing," Luke Zoltan Kelly, a Northwestern University theoretical astrophysicist and NANOGrav researcher, told Space.com. "For most of the community, supermassive black hole binaries are a natural best guess for what's producing the gravitational wave background...." Zoltan Kelley pointed out to Space.com that besides binaries, there are a number of new models in cosmology and in particle physics that, under the right circumstances, could also produce a similar gravitational wave background to that detected by NANOGrav. For example, axion or 'fuzzy' dark matter, cosmic strings, inflationary phase transitions, and many others," the Northwestern astrophysicist said.
"What's really exciting about these possibilities is that each of these models is an attempt to explain some of the biggest current mysteries of our universe."
Re:Now this is a waste of government money (Score:4, Insightful)
Re: (Score:2)
Yeah, like all that quantum crap the government funded. What the 'ell were they thinking?
Re: (Score:2)
A mile is 1.6 km. For any value with resolution less than half a km, miles and kilometres are equivalent.
Hertz is in units of 1/seconds. If you have a frequency that is considerably less than 1 Hz it is not unusual to use the reciprocal, the period, in seconds, instead.
Just missing inductors (Score:4, Funny)
It's just ripples in the power supply that cause some minor output distortion in the simulation's analog outputs. Some engineer thought they could save a few cents by leaving out a couple of chokes. Don't worry. We'll fix it in revision 2.
What's this about 20 light years? (Score:5, Informative)
Re: (Score:2)
I came here to say something similar. I found this and other inaccurate statements just in the summary. For instance:
Frequencies are not measured in units of time - it's one-over-time. The typical unit of measure would be Hz (with appropriate SI-prefixes), which is cycles per second. The milliseconds they mention would be the wave's period - the reciproc
Final Parsec Problem (Score:3)
As best we understand the dynamics of merging galaxies, we have pretty good models for how the supermassive black holes are able to lose orbital energy by flinging away nearby stars - a process called dynamical friction [wikipedia.org]. This energy loss allows the black holes to gradually get closer to each other. But at a certain point, at a distance scale of several lightyears (a parsec), they run out of stars, and we don't know how they lose the remaining energy of their mutual orbit in order to merge. At least, not on the timescale of the universe. Dr. Becky on Youtube, a PhD black hole physicist, recently posted a video about it [youtube.com].
Space (Score:3)
Currently, the primary suspects in this case are pairings of supermassive black holes with masses millions, or even billions, of times that of the sun.
In case we've all forgotten, space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space.
nagging feeling (Score:2)
I have this nagging feeling that one of these days in our bright future, it will be found that all these alleged exotic objects out there never really existed, but were to due to a wrong value for some imputed physical constant.
Re: nagging feeling (Score:1)
It's worse than that. Worse than you can imagine.
No. (Score:2)
From the astrophysicists and other science presenters I follow, the answer is no.
They would explain a lot of it, but the frequency spread seen doesn't properly line up with the predictions. So either there's other things contributing a significant amount to the "hum", or there's a substantial flaw in our prediction of the size distribution of supermassive black holes.
Granted, we do have independent reasons to believe there are some flaws in our predictions - starting with the fact that according to general