TESTING THE SPEED OF GRAVITATIONAL WAVES OVER COSMOLOGICAL DISTANCES

Image: Merging black holes ripple space and time in this artist's concept. Credit: Swinburne Astronomy Productions

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) observed a transient gravitational-wave signal from a black hole-black hole binary (BHBH) inspiral.

The Fermi gamma ray burst monitor revealed the presence of a possible electromagnetic counterpart (Connaughton et al. 2016): a weak transient source above 50 keV, 0.4 s after the GW event was detected with a false alarm probability of 0.0022. The spatial location of both events are poorly determined but mutually consistent.

If the EM and GW signals are related to the same transient phenomenon this opens up a new physical window with which to test the relative speeds of light and gravitational waves.

Several of the alternative theories of gravity invoked to explain the accelerated expansion of the Universe predict c_GW ≠ c_light. In a recent paper (Collett & Bacon 2016) the authors assume that the EM and GW are emitted at the same instant and they obtain a constraint on the ratio of the speeds of light and gravitational waves at the level of 10⁻¹⁷.

The assumption that the electromagnetic and gravitational wave emissions are emitted at the same time is a strong one, so they suggest a method that does not make such an assumption using a strongly lensed GW event and EM counterpart. They show that a single strongly lensed GW event would produce robust constraints at the 10⁻⁷ level, if a high energy EM counterpart is observed within the field-of-view of an observing gamma ray burst monitor.

Collett & Bacon 2016 - Testing the speed of gravitational waves over cosmological distances with strong gravitational lensing (arXiv)
Connaughton et al. 2016 - Fermi GBM Observations of LIGO Gravitational Wave event GW150914 (arXiv)

Comments

SUPERNOVAE FROM WD-WD DIRECT COLLISIONS

Image: Supernova remnant N 63A. Credit: NASA/ESA/HEIC and The Hubble Heritage Team (STScI/AURA) Models for supernovae (SNe) related to thermonuclear explosions of white dwarfs (WDs) have been extensively studied over the last few decades, mostly focusing on single degenerate (accretion of material of a WD) and double degenerate (WD-WD merger) scenarios.

A SIGNIFICATIVE FRACTION OF BARYONS RESIDE IN THE FILAMENTS OF THE COSMIC WEB

(Credit: NASA, ESA, and E. Hallman (University of Colorado, Boulder) Observations of the cosmic microwave background indicate that baryons (protons, neutrons, etc., - the ordinary matter just to understand) occupies only 5% of the total energy content of the Universe (95% is dark matter and dark energy). However in the local universe approximately half of this "ordinary" matter it has never been observed.

Atmospheric Beacons Guide NASA Scientists in Search for Life

Beacons of life could help researchers identify potentially habitable worlds. Credits: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk Some exoplanets shine brighter than others in the search for life beyond the solar system. New NASA research proposes a novel approach to sniffing out exoplanet atmospheres. It takes advantage of frequent stellar storms — which hurl huge clouds of stellar material and radiation into space — from cool, young dwarf stars to highlight signs of habitable exoplanets. Traditionally, researchers have sought potential biosignatures as ways of identifying inhabited worlds: byproducts from life as we know it such as oxygen or methane that over time accumulate in the atmosphere to detectable amounts. But with current technology, according to Vladimir Airapetian, lead author of a Nature Scientific Reports study published on Nov. 2, 2017, identifying these gases on distant terrestrial exoplanets is time-consuming, requiring days of observation time. The ne...

SpaceTime

Search This Blog