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Researchers Believe Rate Of Universe's Expansion Can Be Measured Using Gravitational Waves

Jul 12, 2018 12:59 AM EDT
NASA's Hubble captures this massive globular cluster, a gravitationally bound collection of stars orbiting the Milky Way. New research offers a possible answer to one of the biggest questions in understanding the universe: how fast is it expanding?
(Photo : NASA Goddard Space Flight Center | Flickr)

Scientists uncover the potential key to figuring out one of the great puzzles of the universe: black holes, neutron stars, and gravitational waves they produce.

How Fast Is The Universe Expanding?

Humankind has known for a long time that the universe is in constant expansion since it exploded into life billions of years ago. However, the rate of the universe's expansion, also known as the Hubble constant, remains one of the biggest mysteries in the study of astronomy.

The knowledge of this could not only paint a more accurate picture of the observable universe's origins, but also yield hints on its fate in the far future.

Unfortunately, scientists haven't been able to reach a definitive number of the expansion rate, yet.

According to Phys.Org, many have tried using telescopes to measure the distance between Earth and other cosmic bodies, and how fast it's moving away. However, various efforts have reached different conclusions to the Hubble constant, suggesting that this isn't a precise method of figuring out the expansion rate.

Gravitational Waves Are The Key

In a paper to be published in the journal Physical Review Letters on Thursday, July 12, a pair of scientists reveals that they found a potentially more accurate way to calculate the Hubble constant. This new method includes using gravitational waves from a black hole-neutron star binary, which is a pairing of a spiraling black hole and neutron star.

Phys.Org explains that the duo circle each other, then eventually collide, producing shattering gravitational waves and a blinding flash of light. Scientists could use the light to estimate how fast it's moving away from Earth, then the gravitational waves can provide an independent measurement of the system's distance. The combination of both is expected to offer a more precise measurement of the Hubble constant than the previous efforts.

The problem is, this type of system is rare, especially considering Earth can only observe a limited slice of space.

"Black hole-neutron star binaries are very complicated systems, which we know very little about," lead author Salvatore Vitale, an assistant professor of physics at the Massachusetts Institute of Technology, explains in a statement. "If we detect one, the prize is that they can potentially give a dramatic contribution to our understanding of the universe."

The team uses the Laser Interferometer Gravitational-Wave Observatory or LIGO to detect gravitational waves, which are produced by cataclysmic astrophysical phenomena.

Initially, this method was used in a pair of neutron stars colliding, which produced both the light and strong gravitational waves. However, the results were also greatly uncertain due to the neutron star binary's nature of emitting gravitational waves in an uneven fashion.

While black hole-neutron star binary systems are so much rarer than neutron star binary systems, scientists determined that the former would still yield a more accurate estimate of the Hubble constant.

Vitale says that LIGO will begin collecting data again in January 2019 and the researchers are expecting it to witness at least one black hole-neutron star system.

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