Continuing the search for gravitational waves

March 29, 2016 by Peter Garnavich
Continuing the search for gravitational waves
LBT (Large Binocular Telescope)

In February, the LIGO Scientific Collaboration announced it had detected gravitational waves for the first time, confirming the last prediction of Albert Einstein's theory of relativity. Somewhat overlooked in the excitement that followed is the fact that scientists don't know the exact location the waves were coming from. University of Notre Dame astronomer Peter Garnavich is leading a group of researchers who are hoping to more precisely locate where future gravitational waves originate.

Garnavich and the group are using the LBT (Large Binocular Telescope) in southeastern Arizona to search for visible light emission from the event generating the gravitational waves. Notre Dame owns a share of the LBT project, which consists of two 8.4-meter mirrors and is the world's largest telescope on a single mounting. The team is searching the sky to find the light emitted from supernovae and gamma ray bursts, and now gravitational wave transients.

"Gravitational wave transients are like earthquakes," Garnavich said. "Earthquakes make waves that propagate around and through the earth. A truck hitting a pothole will send out some vibrations, but they won't make it very far. A big earthquake can send waves out that can be felt hundreds of miles away. So these two merging are like a huge earthquake, but instead of the earth shaking, it is space-time vibrating. Advanced LIGO is like a seismograph for space-time."

Garnavich notes that the gravitational waves that the LIGO group detected emanating from two black holes merging were somewhat of a surprise.

"These LIGO black holes are bigger than the stellar black holes we know about in the Milky Way, but much smaller than the massive black holes in the centers of galaxies. This may be as big a discovery as the gravitational waves themselves," Garnavich said. "Black hole mergers are not expected to produce a lot of electromagnetic radiation, and the prevailing consensus was that gravitational waves would be detected from colliding neutron stars, an event that should generate some light."

Garnavich notes that the effort to more precisely locate gravitational waves is akin to searching for a needle in a haystack. The swath of space that LIGO's research identified as a possible location of the event can contain millions of stars and galaxies.

"We hunt for things that snap, crackle or pop in their light output, and that narrows candidates down to maybe 100 across the sky," he said

Garnavich's group is hoping to use the LBT and other observational surveys to identify promising candidates and eliminate not-so-promising ones.

"I hope this LIGO event was the first of many so we can combine and to figure out what are creating these exotic events," he said.

Given past experience, a breakthrough like the LIGO discovery opens the door to even more discoveries. The search Garnavich and his group is undertaking has the potential to provide a new understanding of how the universe works.

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2 / 5 (4) Mar 29, 2016
If the waves are traveling at the speed of light, then how again would researchers locate the source of a signal which is many light years away?
Da Schneib
5 / 5 (3) Mar 29, 2016
This is how LIGO and future similar instruments will enhance astronomy. It's good to see some folks doing exactly the research the data tells them to do.

When we add a third gravitational observatory, hopefully the one India is dithering over, we'll be able to tell the LBT and other instruments right where to look.
1 / 5 (4) Mar 30, 2016
I've been wondering if the GW is coming toward us or away from us. If it's coming toward us, say, in a direct line toward Earth (if that's possible), could it be that it has already or nearly arrived but we aren't able to feel its effects for awhile because Time has passed us by and we are still just catching up to future events that have already happened?
Just a hypothesis of mine.
2.3 / 5 (3) Mar 30, 2016
What does that have to do with Obama?
3 / 5 (2) Mar 30, 2016
If the waves are traveling at the speed of light, then how again would researchers locate the source of a signal which is many light years away?
Do you wait for the 'pop' of a firecracker before throwing it? I'm pretty sure these researchers are sciency enough to look where the next possible candidates might occur.
5 / 5 (1) Mar 30, 2016
If the waves are traveling at the speed of light, then how again would researchers locate the source of a signal which is many light years away?

Like with any other source: Triangulation. This is why there are more LIGO-like stations being set up in addition to the two currently in operation (two already allow for a very rough directional estimate).

Any light that was created at the same time and place as the event will arrive simultaneously (since it's also travelling at c). So where's the problem?

There are wide field (i.e. low resolution) telescopes that look for energetic events which are hooked up to automated messaging systems that let narrow field/high resolution telescopes all over the world know imediately when they find something so these can then be trained on the source within minutes. This has been standard procedure for observing e.g. supernovae in their early strages for quite some years.

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