Gravitational waves can be used as a tool to determine the rate of expansion of the universe


Scientists have conducted studies which have concluded that gravitational waves emitted by a rare system — a hugely energetic pairing of a spiraling black hole and a neutron star — can tell us the rate of the expansion of the universe, which is determined by the Hubble constant.

Ever since the existence of the universe, it has been dragging billions of stars and galaxies along with it as it gradually expands. This has been happening for 13.8 billion years, since the Big Bang.

An accurate way of measuring the Hubble constant

For a lot of years, astronomers have relied on the positioning of certain stars and the speed with which they move away from the earth to measure the expansion rate of the universe but precise readings of these factors have often resulted in different values of the constant.

The scientists from Massachusetts Institute of Technology (MIT) and Harvard University have now proposed a more accurate way of measuring the Hubble constant. This method suggests using gravitational waves emitted by a relatively rare system: a black hole-neutron star binary.

How gravitational waves can give more precise results

According to the study published in the journal Physical Review Letters, as the objects in the universe circle in towards each other, they produce strong gravitational waves and finally, a flash of light when they collide.

This light can be an indicator of the system’s velocity with which it is moving away from the earth, giving a more precise and independent measure of the system’s distance.

Even though there is a rarity of black hole-neutron star binaries, researchers calculate that detecting even a few should yield the most accurate value yet for the Hubble constant and the rate of the expanding universe.

Lack of information about Black hole-neutron star binaries

Recently, the value of Hubble constant was measured using NASA’s Hubble Space Telescope and the European Space Agency’s Planck satellite and both had observations based on a type of star known as a Cepheid variable, as well as on observations of supernovae.

Both these measurements were extremely precise but their estimations of the Hubble constant disagree significantly. Hence, the scientists are trying to rely on gravitational waves, even though there is not sufficient information.

“Black hole-neutron star binaries are very complicated systems, which we know very little about. If we detect one, the prize is that they can potentially give a dramatic contribution to our understanding of the universe,” said Salvatore Vitale, Assistant Professor at MIT.

While scientists research more about this topic, other methods are being used to determine the expansion of the universe.

These methods include the observations of the fluctuations in the cosmic microwave background the electromagnetic radiation that was left over in the immediate aftermath of the Big Bang, when the universe was still in its infancy.

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