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Why are LIGO and Virgo not mechanically capable of detecting the collisions of supermassive black holes? Is it because the amplitude is so big it "pegs the nee

Why are LIGO and Virgo not mechanically capable of detecting the collisions of supermassive black holes? Is it because the amplitude is so big it "pegs the needle" above its limit?

privong 6y ago
LIGO and VIRGO are sensitive to gravitational waves within a specific frequency range. The bulk of GW energy is emitted at a frequency that is twice the orbital frequency of the objects emitting the gravitational waves. Supermassive black holes are sufficiently large that they merge before they could have an orbit compact enough to emit gravitational waves at high enough frequencies for LIGO and VIRGO to detect them. Less massive compact objects are smaller and so can reach higher orbital frequencies before merging.
- 7373737373 6y ago
  There seem to be projects for lower frequencies/longer wavelengths underway: https://youtu.be/GlmMxmWHEfg?t=3733 https://youtu.be/GlmMxmWHEfg?t=3733
  - thunderrabbit 6y ago
    Cool!
- thunderrabbit 6y ago
  Oh wow so it's exactly the opposite of my guess. Thank you for your explanation. It now makes perfect sense to me that more massive objects wouldn't revolve quickly enough to create high frequency waves.
hatsuseno 6y ago
Your reasoning is on the right track, but it's the wavelength specifically that's outside of the range for both Virgo and LIGO. As far as I understand the subject, we're running into physical limits for their detection using that kind of experiment. Instead, research is attempting to infer the mergers using pulsar Doppler shift measurements.
joeberon 6y ago
The low frequency noise is very bad for ground-based gravitational-wave interferometers. For example, seismic noise from ground motion, such as waves hitting the west coast for LIGO Hanford, or logging operations for LIGO Livingston; also the control noise is really bad at low frequencies. Generally most noises apart from the quantum noise scale inversely to the frequency. The ground-based detectors are most sensitive at 100Hz, which is around the frequency of the binary black hole inspiral. Supermassive black holes are more like millihertz. We do not have any concrete way yet to measure the gravitational waves from supermassive black holes, but there are some ideas. For example we can look at the time dilation of frequencies of nearby pulsars (https://en.wikipedia.org/wiki/Pulsar https://en.wikipedia.org/wiki/Pulsar) as a kind of gravitational wave interferometer in space, however to get a signal-to-noise ratio greater than one many years (decades) of data is needed.

Why are LIGO and Virgo not mechanically capable of detecting the collisions of supermassive black holes? Is it because the amplitude is so big it "pegs the needle" above its limit?

privong 6y ago

LIGO and VIRGO are sensitive to gravitational waves within a specific frequency range. The bulk of GW energy is emitted at a frequency that is twice the orbital frequency of the objects emitting the gravitational waves. Supermassive black holes are sufficiently large that they merge before they could have an orbit compact enough to emit gravitational waves at high enough frequencies for LIGO and VIRGO to detect them. Less massive compact objects are smaller and so can reach higher orbital frequencies before merging.

7373737373 6y ago
There seem to be projects for lower frequencies/longer wavelengths underway: https://youtu.be/GlmMxmWHEfg?t=3733 https://youtu.be/GlmMxmWHEfg?t=3733
- thunderrabbit 6y ago
  Cool!
thunderrabbit 6y ago
Oh wow so it's exactly the opposite of my guess. Thank you for your explanation. It now makes perfect sense to me that more massive objects wouldn't revolve quickly enough to create high frequency waves.

hatsuseno 6y ago

Your reasoning is on the right track, but it's the wavelength specifically that's outside of the range for both Virgo and LIGO. As far as I understand the subject, we're running into physical limits for their detection using that kind of experiment. Instead, research is attempting to infer the mergers using pulsar Doppler shift measurements.

joeberon 6y ago

The low frequency noise is very bad for ground-based gravitational-wave interferometers. For example, seismic noise from ground motion, such as waves hitting the west coast for LIGO Hanford, or logging operations for LIGO Livingston; also the control noise is really bad at low frequencies. Generally most noises apart from the quantum noise scale inversely to the frequency. The ground-based detectors are most sensitive at 100Hz, which is around the frequency of the binary black hole inspiral. Supermassive black holes are more like millihertz. We do not have any concrete way yet to measure the gravitational waves from supermassive black holes, but there are some ideas. For example we can look at the time dilation of frequencies of nearby pulsars (https://en.wikipedia.org/wiki/Pulsar https://en.wikipedia.org/wiki/Pulsar) as a kind of gravitational wave interferometer in space, however to get a signal-to-noise ratio greater than one many years (decades) of data is needed.