Amateur Astronomy

Join us for the host galaxy hunting and kilonova signature of gravitational waves event in 2019 !

The host galaxy NGC4993 of the gravitational signal detected on August 17th 2017 from the merger of two neutrons stars !

Since 2015, gravitational waves (GW), ripples in space and time, have been detected by the LIGO and Virgo collaboration. The most promising astrophysical events able to emit gravitational waves are the binary coalescence of compact objects, which involves black holes and neutron stars. After the discovery of many black holes the last three years, a new phenomenon has been discovered by LIGO/Virgo on August 17th 2017, leading to a turn over in gravitational astronomy. Indeed, for the first time, a gravitational signal was detected from the coalescence of two neutrons stars as well as a gamma-ray burst signal from the Fermi/GBM space instrument. But this is not the end of the story…. 12 hours after the gravitational wave a bright optical and near-infrared source was detected in the galaxy NGC4993, located in the gravitational-wave sky localization by telescopes on ground. This leads to an impressive multi-wavelength follow-up campaign on the ground and in space and during several weeks. It was the first time that this optical phenomenon, so called kilonova, was clearly observed. Kilonovae originate from neutron-rich outflows expulsed after the merger which emit from UV to infrared emission powered by the radioactive decay of r-process elements. These elements are the heaviest elements produced in the Universe for which the origin was not known until now (but this origin was predicted by models) !

For the next observational campaign of LIGO/Virgo (O3, early 2019), open public alerts will be released to the scientific community in case of detection of gravitational waves. If the alert corresponds to a systems including a neutron star, we still expect such optical signature associated to a kilonova. Nevertheless, this “new object” appearing in the sky is difficult to find: the sky localization area given by GW detection varies from dozen of square degrees to hundreds of square degrees. The shape of these sky localization areas are usually elongated as a “banana” shape (see video below). Thus, many host galaxies and sources remain compatible with the GW signal. A huge observational effort is needed and the sucess of the GW science is also highly related to ability of the astronomers to detect the EM counterpart from such non-photonic events. Keep watching the sky and stay tuned with GRANDMA !

Here we propose to the astronomical community to join the adventure with GRANDMA, observing some galaxy located in the search area of a given GW alert, to identify the optical signature:

Catch the kilonova signal (click here)

If you have a telescope (> 16 mag in 10 min), let’s join here and be ready for 2019 !

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