Where are the Gravity Waves?

[Peron]

LIGO (Laser Interferometer Gravitational-Wave Observatory) has been built and works perfectly fine. But why hasn't it detected any gravity waves?

 

Isnt PSR B1913+16 the binary system, indirect evidence that gravity waves exist? So why not point ligo in that direction?

[swansont]

I'm guessing it's because the system is 21,000 LY from earth, and any signal would be too faint to be detected.

 

http://www.johnstonsarchive.net/relativity/binpulsar.html

 

The null result was expected, and puts limits on some quantities/models.

http://scienceblogs.com/catdynamics/2009/08/cosmological_gravitational_rad.php

http://www.space.com/scienceastronomy/090819-gravitational-waves.html

Edited October 19, 2009 by swansont

[toastywombel]

There have been observations of gravitational waves from LIGO. This is from Wikipedia,

 

"In February 2007, GRB 070201, a short gamma-ray burst, arrived at Earth from the direction of the Andromeda Galaxy, a nearby galaxy. The prevailing explanation of most short gamma-ray bursts is the merger of a neutron star with either a neutron star or black hole. LIGO reported a non-detection for GRB 070201, ruling out a merger at the distance of Andromeda with high confidence. Such a constraint is predicated on LIGO eventually demonstrating a direct detection of gravitational waves."

 

Furthermore LIGO is described as "not a one-shot experiment". There are constant modifications being made to detect these small bends in light caused by bends in space time that signal gravitational waves. We will probably have to be a little patient until the boys up at Caltech and MIT perfect this technology

 

The reason we may have not found gravitational waves from the system you mentioned is, just like swansont said, it is too far away. The further away these systems are the lower the frequency of there gravitational waves. It is impossible to view gravitational waves outside a specific frequency set.

 

Also from Wikipedia,

 

"Stephen W. Hawking and Werner Israel list different frequency bands for gravitational waves that could be plausibly detected, ranging from 10-7 Hz up to 1011 Hz.[2]"

 

Anything outside those frequencies are thought to be impossible to detect.

 

Here are some links you might find useful.

http://en.wikipedia.org/wiki/Gravitational_wave

http://en.wikipedia.org/wiki/LIGO

http://ligonews.blogspot.com/

 

Hope this helps

[swansont]

There have been observations of gravitational waves from LIGO. This is from Wikipedia,

 

"In February 2007, GRB 070201, a short gamma-ray burst, arrived at Earth from the direction of the Andromeda Galaxy, a nearby galaxy. The prevailing explanation of most short gamma-ray bursts is the merger of a neutron star with either a neutron star or black hole. LIGO reported a non-detection for GRB 070201, ruling out a merger at the distance of Andromeda with high confidence. Such a constraint is predicated on LIGO eventually demonstrating a direct detection of gravitational waves."

 

This was a non-detection event, though. A GRB is not something LIGO detects, so LIGO provisionally ruled out the burst as having come from Andromeda, since there was no corresponding gravitational signal.

[toastywombel]

Oh I see, so a gamma-ray burst is a sign of a possible gravitational wave, but not evidence of one.

[swansont]

Oh I see, so a gamma-ray burst is a sign of a possible gravitational wave, but not evidence of one.

 

In this case, it is thought that the GRB would also emit gravitational waves, but since LIGO detected nothing, the source must have been farther away than Andromeda, even though it came from that direction. But LIGO must eventually detect something to fully corroborate this. You detect nothing if the machine doesn't work, and you have to exclude that possibility. IOW, measuring a false null result is easy, and you need confirmation that it was a real null result.

[Peron]

Exactly you cant use the detection of nothing as evidence. When Advance LIGO is built, maybe this will be confirmed.

[swansont]

Exactly you cant use the detection of nothing as evidence.

 

Yes, you can, but you have to be very careful about it.

 

When Advance LIGO is built, maybe this will be confirmed.

That's the gist of it.