Astronomers Determined The Real Value Of The Hubble Constant

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In August 2017, two neutron stars were involved in an impact. Astronomers closely watched the collision all around the globe. Recently, experts were able to use the data collected during this event to refine the Hubble Constant, one of the essential characteristics of the universe.

Scientists calculated the Hubble Constant

The Hubble Constant is the value that represents the rate at which the universe expands. However, throughout the history of space observation, the measurements sometimes showed discrepancies, and scientists were not able to come up with an explanation for it.
The Planck satellite gathered data that indicated the Hubble Constant should be 67.4 kilometers per second per megaparsec.

Another way to measure it is by studying the nebulae left behind after the death of Type Ia supernovae stars. This method was used recently to measure the Hubble Constant and showed a result of 72.78 kilometers per second per megaparsec. A more recent approach uses luminosity of Cepheid variable stars to calculate distance. Yet again, the Hubble Constant shows a different value, suggesting an even faster expansion rate.

The scientists studied the movements of 70 Cepheid variables that returned the result of 74.03 kilometers per second per megaparsec. As we can see, measuring the Hubble Constant is quite a dilemma. Fortunately, the collision of the two neutron stars offered scientists a new attempt at obtaining the correct result.

Hubble Constant revealed thanks to a neutron stars collision

The event, named GW170817, allowed astronomers to observe a collision between two neutron stars, taking into consideration multiple perspectives like gravitational wave astronomy, optical astronomy, and radio astronomy. According to experts, neutron stars collisions usually emit a large amount of energy. The two massive neutron stars whip around each other at unimaginable speeds, producing an enormous blast.

“This burst of gravitational waves can be used as a ‘standard siren’: based on the shape of the gravitational wave signal, we can tell how ‘bright’ the event should have been in gravitational waves. We can then take how bright the event was actually seen to be, and work out what the distance must have been.”

However, astronomers can only achieve this if they know the orientation of the event, which requires more data. Using the data collected during the collision, scientists were able to calculate the direction of the stars, which allowed them to determine the precise distance. The collision took place in a galaxy 130 million light-years away. Using this knowledge, the team was able to figure out the correct value of the Hubble Constant, which is 70.3 kilometers per second per megaparsec.

Doris’s passion for writing started to take shape in college where she was editor-in-chief of the college newspaper. Even though she ended up working in IT for more than 7 years, she’s now back to what he always enjoyed doing. With a true passion for technology, Doris mostly covers tech-related topics.