(ORDO NEWS) — Scientists have proposed a new way to measure the rate of expansion of the universe based on the joint observation of gravitational waves and light signals arising from the collision of black holes and neutron stars. The article was published in the journal Physical Review Letters.
The rate of expansion of the Universe, one of the key parameters of cosmology, is estimated by astrophysicists using a coefficient that links the distance to any extragalactic object with the rate of its removal – the Hubble constant. In its physical essence, this is a local acceleration.
Traditionally, scientists use two methods to evaluate it. The first is based on the analysis of fluctuations of the cosmic microwave background – the relic radiation left over from the Big Bang; and the second – on the accidental appearance of supernovae in distant galaxies. According to the first method, the value of the Hubble constant is 67.4, and the second – 74 kilometers per second per megaparsec. Naturally, astronomers are concerned about this serious discrepancy and are constantly looking for new ways to measure.
Researchers from the UK, Sweden and the Netherlands have proposed a method based on the joint observation of explosions of light and gravitational ripples in the tissue of space, caused by collisions of a black hole and a neutron star. The authors simulated 25 thousand such collisions on a computer and found that by 2030 gravitational-wave observatories will be able to sense ripples in space-time from three thousand of them, and in about a hundred such cases, telescopes will also see accompanying explosions of light.
Scientists believe that this data will be enough to provide a new, completely independent measurement of the rate of expansion of the universe, accurate and reliable enough to confirm or deny the need to create new physics.
“The collision of a neutron star with a black hole is a catastrophic event that causes ripples in spacetime known as gravitational waves, which we can now detect on Earth with observatories such as LIGO and Virgo,” University College London said in a press release. by astrophysicist Stephen Feeney – We have never seen light from such collisions, but increasing the sensitivity of gravitational wave equipment, together with new detectors in India and Japan, will lead to a huge leap forward in terms of how much we will be able to detect such events. It is incredibly interesting and should open a new era in astrophysics. “
To calculate the Hubble constant, you need to know the distance to astronomical objects, as well as the speed at which they are moving away. Analysis of gravitational waves shows how far to the collision site. To determine how fast the colliding galaxy is receding, astronomers measure the redshift, which is how the wavelength of light produced by a source stretches as it moves. According to the authors, the explosions of light accompanying the collisions will make it possible to accurately determine the redshift of the galaxy in which the collision occurred.
“If our assumptions are correct, many of these collisions will not cause explosions – the black hole will swallow the star without leaving a trace. But in some cases, the small black hole will first explode the neutron star before swallowing it up, leaving the matter outside the hole, which emits electromagnetic radiation “- continues Dr. Feeney.
Of the two existing options for estimating the expansion rate of the Universe, the “stellar” method is more convenient, since, unlike the measurement of the microwave background, it does not need to use the complete theory of the Universe. However, in order to decide which of the two methods is more accurate, at least one more independent verification method is needed, which, according to the authors, can be the method they proposed.
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