- Recently, LIGO Scientific Collaboration (LSC) has made the discovery of gravitational waves from a pair of neutron star-black hole (NS-BH) mergers.
- The reverberations from these two objects were picked up using a global network of gravitational wave detectors, the most sensitive scientific instruments ever built.
- Until now, the LIGO-Virgo Collaboration (LVC) was only able to observe collisions between pairs of black holes or neutron stars. The NS-BH merger is a hybrid collision.
Black Hole
- A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space.
- Gravitational waves are created when two black holes orbit each other and merge.
- Neutron stars comprise one of the possible evolutionary end-points of high mass stars.
- Once the core of the star has completely burned to iron, energy production stops and the core rapidly collapses, squeezing electrons and protons together to form neutrons and neutrinos.
- A star supported by neutron degeneracy pressure is known as a ‘neutron star’, which may be seen as a pulsar if its magnetic field is favourably aligned with its spin axis.
Important points::
These are invisible ripples in space that form when:
- A star explodes in a supernova.
- Two big stars orbit each other.
- Two black holes merge.
Neutron star-Black hole (NS-BH) merges.
- They travel at the speed of light (1,86,000 miles per second) and squeeze and stretch anything in their path.
- As a gravitational wave travels through space-time, it causes it to stretch in one direction and compress in the other.
- Any object that occupies that region of space-time also stretches and compresses as the wave passes over them, though very slightly, which can only be detected by specialized devices like LIGO.
Theory and Discovery:
- These were proposed by Albert Einstein in his General Theory of Relativity, over a century ago.
- However, the first gravitational wave was actually detected by LIGO only in 2015.
- As the two compact and massive bodies orbit around each other, they come closer, and finally merge, due to the energy lost in the form of gravitational waves.
- The Gravitational Waves signals are buried deep inside a lot of background noise. To search for the signals, scientists use a method called matched filtering.
- In this method, various expected gravitational waveforms predicted by Einstein’s theory of relativity, are compared with the different chunks of data to produce a quantity that signifies how well the signal in the data (if any) matches with any one of the waveforms.
- Whenever this match (in technical terms “signal-to-noise ratio” or SNR) is significant (larger than 8), an event is said to be detected.
- Observing an event in multiple detectors separated by thousands of kilometers almost simultaneously gives scientists increased confidence that the signal is of astrophysical origin.
Importance of Discovery:
- A neutron star has a surface and black hole does not. A neutron star is about 1.4-2 times the mass of the sun while the other black hole is much more massive. Widely unequal mergers have very interesting effects that can be detected.
- Inferring from data as to how often they merge will also give us clues about their origin and how they were formed.
- These observations help us understand the formation and relative abundance of such binaries.
- Neutron stars are the densest objects in the Universe, so these findings can also help us understand the behaviour of matter at extreme densities.
- Neutron stars are also the most precise ‘clocks’ in the Universe, if they emit extremely periodic pulses.
- The discovery of pulsars going around Black Holes could help scientists probe effects under extreme gravity.
LIGO Scientific Collaboration (LSC):
- LSC was founded in 1997 and currently made up of more than 1000 scientists from over 100 institutions and 18 countries worldwide.
- It is a group of scientists focused on the direct detection of gravitational waves, using them to explore the fundamental physics of gravity, and developing the emerging field of gravitational wave science as a tool of astronomical discovery.
- The LSC carries out the science of the LIGO Observatories, located in Hanford, Washington and Livingston, Louisiana as well as that of the GEO600 detector in Hannover, Germany.
LIGO-India Project
- The LIGO-India observatory is scheduled for completion in 2024, and will be built in the Hingoli District of Maharashtra.
- LIGO India is a planned advanced gravitational-wave observatory to be located in India as part of the worldwide network.
- The LIGO project operates three gravitational-wave (GW) detectors.
- Two are at Hanford in the State of Washington, north-western USA, and one is at Livingston in Louisiana, south-eastern USA.
- The LIGO-India project is an international collaboration between the LIGO Laboratory and three lead institutions in the LIGO-India consortium: Institute of Plasma Research, Gandhinagar; IUCAA, Pune; and Raja Ramanna Centre for Advanced Technology, Indore.
- It will significantly improve the sky localisation of these events.
- This increases the chance of observation of these distant sources using electromagnetic telescopes, which will, in turn, give us a more precise measurement of how fast the universe is expanding.
SOURCE: THE HINDU,THE ECONOMIC TIMES,MINT