Astronomy Current Affairs

Scientists detect Gravitational waves for fourth time

Scientists have successfully detected gravitational waves for fourth time coming from merger of two massive black holes. It was for first time, these waves were simultaneously detected by US-based Laser Interferometer Gravitational-wave Observatory (LIGO) and Italy-based Virgo detectors. The first two detection were made in September and December 2015 in quick succession and for third time it was detected in January 2017.

Key Facts

The recently detected gravitational waves were emitted during final moments of merger of two black holes  located about 1.8 billion light-years away with masses about 31 and 25 times mass of Sun. The newly produced spinning black hole has about 53 times mass of our sun i.e. about 3 solar masses were converted into gravitational-wave energy during merger.

Gravitational Waves

Gravitational waves are ripples curvature of spacetime which propagate as waves, travelling outward from source at the speed of light. They transport energy as gravitational radiation and pass through matter without interacting with it. Gravitational waves were first predicted in 1916 by Albert Einstein on the basis of his Theory of General Relativity. Strongest sources of gravitational waves are among enigmatic objects in our universe like black holes, supernova, neutron stars and Big Bang. Information extracted by these transmitted waves may help to address unsolved questions and mysteries of physics and astronomy.

Note: Russel Hulse and Joseph Taylor had discovered indirect evidence for existence of gravitational waves emitted from decaying orbital period of objects called binary pulsars in 1974,. Both of them for their discovery were awarded the Nobel Prize in Physics in 1993.


Osiris-Rex: NASA’s asteroid-bound spacecraft swings by Earth

NASA’s asteroid-chasing spacecraft Osiris-Rex successfully swung by Earth to put it on desired trajectory towards near earth asteroid Bennu using Earth’s gravity. It passed within 17,237 kilometres from Earth above Antarctica.

During closest flyby, Osiris-Rex’s science instruments were tested by scanning Earth and moon as a practice for its operations at Bennu.


The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) mission was launched in September 2016 for studying 101955 Bennu, a carbonaceous asteroid. It is NASA’s first asteroid sampling mission. Japan already has visited an asteroid and returned some specks.

The spacecraft will reach small, roundish asteroid in 2018 and return to Earth after collecting some of its gravels by 2023. It will capture 2 ounces of dust on asteroid using its robotic arm without landing i.e. by hovering like a hummingbird stirred up by nitrogen gas thruster  and then begun its return trip to earth.

101955 Bennu is near-Earth carbonaceous asteroid about the size of a small mountain in the Apollo group. It was discovered in September 1999 by the LINEAR Project.

Significance of mission

NASA scientists believe that Bennu asteroid holds clues to origin of solar system and life and source of water and organic molecules found on Earth. Material returned from asteroid is expected to enable scientists to learn more about the formation and evolution of the Solar System. It will also give insights of initial stages of planet formation and the source of organic compounds which led to the formation of life on Earth.