Successful detection of gravity waves!

[Dannyalcatraz]

Note that it is a very tiny wave. The arms of LIGO are kilometers long, and the change in length observed was less than the diameter of a typical atom.

That's probably about the right size for me to surf, TBH.

 

[freyar]

Hi,

Are there any frameworks that this breaks? Any theoreticians who are not happy about this result?

Is there any "new" result here? The result seems to be exactly what was predicted, meaning, it confirms an already presumed theory, and maybe doesn't add a lot which is new?

Thx!
TomB

I can't think of a reason anyone would be unhappy about this. This comes from the part of "theory space" where we know Einstein's general relativity works for other reasons, so even modified gravity theories should have predicted this, or at least something close enough that this single measurement wouldn't be enough to distinguish.

As for new, well, the new part is that we have proven we can measure gravitational waves directly! I think it's a bit hyperbolic to say it's like when Galileo first used a telescope to look at Jupiter, but it's certainly as big of a deal as when we turned on the first radio telescope or x-ray telescope. But, in a sense, you're right, this isn't new in terms of changing what we think about how gravity works. The new science it brings --- which will be a whole lot! --- is our understanding of what's out there in space, especially extreme conditions like colliding black holes. And, eventually, that might give us some hints about gravity beyond GR. So, even though this isn't quite related to my work, I'm very excited about the possibilities we now have with a whole new way to look at the cosmos.

 

[tomBitonti]

I can't think of a reason anyone would be unhappy about this. This comes from the part of "theory space" where we know Einstein's general relativity works for other reasons, so even modified gravity theories should have predicted this, or at least something close enough that this single measurement wouldn't be enough to distinguish.

As for new, well, the new part is that we have proven we can measure gravitational waves directly! I think it's a bit hyperbolic to say it's like when Galileo first used a telescope to look at Jupiter, but it's certainly as big of a deal as when we turned on the first radio telescope or x-ray telescope. But, in a sense, you're right, this isn't new in terms of changing what we think about how gravity works. The new science it brings --- which will be a whole lot! --- is our understanding of what's out there in space, especially extreme conditions like colliding black holes. And, eventually, that might give us some hints about gravity beyond GR. So, even though this isn't quite related to my work, I'm very excited about the possibilities we now have with a whole new way to look at the cosmos.

Hi,

Thanks!

I was thinking that this would give us new data about high mass events (black hole and neutron star mergers), so an exciting new window for astronomy.

Do you know if there is any hope to match the detection with other data (EM radiation from the same event)? I'd be curious about matching that to the gravity wave detection, and what that tells us.

Thx!
TomB

 

[Umbran]

I was thinking that this would give us new data about high mass events (black hole and neutron star mergers), so an exciting new window for astronomy.

Yes, that's the major gain here. In terms of new science, it gives us a window into the details of astronomical events.

Basically, it is like having a new telescope - the fact that the telescope works isn't itself really a surprise or reveals new sceince, but what the new telescope *looks* at is amazing.

Do you know if there is any hope to match the detection with other data (EM radiation from the same event)? I'd be curious about matching that to the gravity wave detection, and what that tells us.

With merging black holes, I don't think you're expecting much other radiation from the event. You get a lot of mass converted to energy (the power here is enormous - about three solar masses converted to gravity waves in the course of tenths of a second, if I recall the estimates correctly), but all that mass is already behind event horizons, so it all comes off as gravity waves, not as light or other particles.

From merging neutron stars, you may get a much different result in terms of other observable results, as there's no even horizon in the way (at least for the start of the event).

But note that the gravitational waves are moving at the speed of light - so they arrive at the same time as the light. You'd have to have a telescope that just happened to be looking at the right portion of the sky to see it. And the thing was about a billion light years away, so you're talking deep field stuff, not just inside our galaxy.

 

[tuxgeo]

. . . and this is the new, improved LIGO that detected this -- not the original LIGO they built the first time.

Q1: How many more billions of $$ are going to need to be spent to built even more-sensitive instruments that can pick up on smaller events? (There are sure to be smaller events, right?)

Q2: Are different frequencies of lasers needed to build the more-sensitive instruments?

 

[freyar]

With merging black holes, I don't think you're expecting much other radiation from the event. You get a lot of mass converted to energy (the power here is enormous - about three solar masses converted to gravity waves in the course of tenths of a second, if I recall the estimates correctly), but all that mass is already behind event horizons, so it all comes off as gravity waves, not as light or other particles.

From merging neutron stars, you may get a much different result in terms of other observable results, as there's no even horizon in the way (at least for the start of the event).

But note that the gravitational waves are moving at the speed of light - so they arrive at the same time as the light. You'd have to have a telescope that just happened to be looking at the right portion of the sky to see it. And the thing was about a billion light years away, so you're talking deep field stuff, not just inside our galaxy.

Right, for merging black holes, you wouldn't expect to see anything else. For merging neutron stars, you would expect to see a lot of light, actually. I don't know the detailed numbers, but it's a little more optimistic than Umbran mentions, though. You see, the matter in the colliding neutron stars is so dense that the light would take a while (probably a few hours) to work its way out, so the light flash would probably be delayed compared to the gravitational waves (at least this is true of supernovae, which are similar but actually less extreme --- the light flash comes after the neutrino flash). This is actually extremely interesting, as there are astrophysical phenomena called gamma ray bursts that we know are (1) extremely far away and (2) extremely energetic that have been postulated to be neutron star mergers. A major science goal would be to correlate a gamma ray burst with a gravitational wave signature to confirm (or disprove) that hypothesis. Fortunately, there are some gamma ray telescopes that are nondirectional or at least have a wide field of view.

 

[Umbran]

. . . and this is the new, improved LIGO that detected this -- not the original LIGO they built the first time.

And, to be fair, it isn't like they didn't know that. The science of characterizing what the waves should look like was rather ahead of the tech for building the detector. Part of the point, as I understand it, was to get practice and learn with the first version (and just in case there was a more nearby event that they could catch - this one was an estimated billion light years away). My understanding is that the upgrade was part of the plan.

Q1: How many more billions of $$ are going to need to be spent to built even more-sensitive instruments that can pick up on smaller events? (There are sure to be smaller events, right?)

Sure, there will be smaller events. Or more distant ones. But as we learn, we also improve detectors, being able to do more with less...

But, as to yoru question - how many more billions of dollars - over what timespan? We're going to be doing astronomy hopefully forever.

Q2: Are different frequencies of lasers needed to build the more-sensitive instruments?

I'm not sure on that point. I don't think the laser frequency is the real issue. I think power output and mirror quality are more likely to be the important bits.

 

[freyar]

. . . and this is the new, improved LIGO that detected this -- not the original LIGO they built the first time.

Well, very few people expected the original LIGO to see anything. It was generally considered as a proof of technology that might get lucky. It's only now with advanced LIGO that the community would have been surprised not to see something (though this was quite soon).

Q1: How many more billions of $$ are going to need to be spent to built even more-sensitive instruments that can pick up on smaller events? (There are sure to be smaller events, right?)

LIGO is scheduled to undergo some small improvements (not large scale) that will nonetheless improve the performance a lot. Another observatory will open in Italy within I think the next year. Japan and India are also building observatories. My understanding is that these costs are basically already budgeted, so I don't know if you'd count that as new money or not. There are hopes to build a space-based gravitational wave telescope, but it's uncertain that will happen -- it's currently a European project slated to launch in the 2030s, and the one cost estimate I saw is between 1 and 2 billion euros.

However, there is new technology developed for these observatories, which seems likely (as supported by history) to pay back the investment in the future. And a lot of the cost goes to pay for graduate students (about $100,000-200,000 per student), but each of those new PhDs has been estimated to be worth an extra $2-3 million to the economy over their lifetime. And all that is completely neglecting the fact that looking into nature is what humans do.

Q2: Are different frequencies of lasers needed to build the more-sensitive instruments?

That I don't know for sure, but I don't think so. The big challenge is making the system extremely stable. Some of that is making sure the laser system is stable, which may in fact be determined by the lasing material. That also affects the frequency. Anyway, there may be other reasons for choosing a particular laser frequency, but that's well beyond my area of expertise.

 

[freyar]

Do you know if there is any hope to match the detection with other data (EM radiation from the same event)? I'd be curious about matching that to the gravity wave detection, and what that tells us.

And, in fact, there is a paper released today stating that the Swift gamma ray telescope actually did look in the direction the gravitational wave signal came from (even for this first event!) right after LIGO detected it. It didn't see anything, but that's maybe not too surprising for a black hole merger. It would be very interesting to look at a double-neutron star merger.

 

[tomBitonti]

Hi,

Was just wondering: What is the eventual fate of the energy emitted as gravitational radiation by an event like this? Does it mostly radiate into the background, never to interact with matter, always to remain as a ripple in spacetime?

If most matter eventually goes through this sort of process, what percentage of energy will eventually be converted to gravity waves? This one event had about a 5% conversion rate. If we look at one of the big (billion solar mass+) black holes at the centers of galaxies, depending on the sequence of mergers which happened, a big percentage of the mass energy of the black hole might have been radiated away.

Though, the milky way galaxy is estimated at about 10^12 solar masses (1 trillion), so that's a small percentage of the milky way mass lost.

Thx!
TomB

Edit: While googling the above, I found this, which was a good read:

Energy Losses and Gravitational Radiation
https://www.astro.umd.edu/~miller/teaching/astr680s09/lecture04.pdf

From:

ASTR 680, High Energy Astrophysics
https://www.astro.umd.edu/~miller/teaching/astr680s09/

From:

Cole Miller, Department of Astronomy, University of Maryland