What is Hubble Constant?
On the basis of one such observation, scientists have hoped that the expansion of the universe will also be understood. Indeed, as the universe expands, galaxies move away from the Earth. The speed with which they move away from the earth depends on the distance between them and the earth. The relationship between these is called Hubble constant. It was first calculated by the American astronomer Edwin Hubble in 1920 and that is why it is named after him. Many researchers have accurately measured the Hubble constant based on the flickering of the Cepheids stars, but in a different way, the second value is derived based on the cosmic microwave background produced 3.8 million years after the Big Bang. Because of this, there is no consensus among scientists.
Waves emanating from the collision
Physicist Sohrab Bourhanian of the State University of Pennsylvania has told Live Science, “Gravitational waves give a different handle to the Hubble constant.” When massive black holes or neutron stars collide, gravitational waves are emitted. Since 2015, the US Laser Interferometer Gravitational Wave Observatory (LIGO) and its European partner Virgo have tried to detect such signals. Scientists calculate from their sound where the collision must have occurred. Many times the light emanating from it is visible to the telescopes, which can be used to detect how fast they are going.
How will dark sirens answer?
Physicists calculated the value of the Hubble constant when in 2017, the signal was detected by LIGO when two neutron stars collided for the first time. However, the scope of error in this is something that is similar to the brightness of the stars and the results from the CMB. It is believed that after at least 50 more such incidents, the exact Hubble constant will be found. This can be done quickly with the help of Dark Siren. Actually, they are not associated with the brightness of the light. It is believed that with the upgrade to the detector of LIGO in the next five years, more information about these waves will be collected. Sohrab states that Hubble constant can be accurately calculated with the help of a signal instead of 50 that is produced by collisions in objects of large, fast and varying mass.