Archives For October 2017
On 17 August 2017 the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo Interferometer both alerted astronomical observers all over the globe about the detection of a gravitational wave event named GW170817. About two seconds after the detection of the gravitational wave, ESA’s INTEGRAL telescope and NASA’s Fermi Gamma-ray Space Telescope observed a short gamma-ray burst in the same direction.
In the night following the initial discovery, a fleet of telescopes started their hunt to locate the source of the event. Astronomers found it in the lenticular galaxy NGC 4993, about 130 million light-years away. A point of light was shining where nothing was visible before and this set off one of the largest multi-telescope observing campaigns ever — among these telescopes was the NASA/ESA Hubble Space Telescope
Several different teams of scientists used Hubble over the two weeks following the gravitational wave event alert to observe NGC 4993. Using Hubble’s high-resolution imaging capabilities they managed to get the first observational proof for a kilonova, the visible counterpart of the merging of two extremely dense objects — most likely two neutron stars. Such mergers were first suggested more than 30 years ago but this marks the first firm observation of such an event. The distance to the merger makes the source both the closest gravitational wave event detected so far and also one of the closest gamma-ray burst sources ever seen.
“Once I saw that there had been a trigger from LIGO and Virgo at the same time as a gamma-ray burst I was blown away,” recalls Andrew Levan of the University of Warwick, who led the Hubble team that obtained the first observations. “When I realised that it looked like neutron stars were involved, I was even more amazed. We’ve been waiting a long time for an opportunity like this!”
Hubble captured images of the galaxy in visible and infrared light, witnessing a new bright object within NGC 4993 that was brighter than a nova but fainter than a supernova. The images showed that the object faded noticeably over the six days of the Hubble observations. Using Hubble’s spectroscopic capabilities the teams also found indications of material being ejected by the kilonova as fast as one-fifth of the speed of light.
“It was surprising just how closely the behaviour of the kilonova matched the predictions,” said Nial Tanvir, professor at the University of Leicester and leader of another Hubble observing team. “It looked nothing like known supernovae, which this object could have been, and so confidence was soon very high that this was the real deal.”
Connecting kilonovae and short gamma-ray bursts to neutron star mergers has so far been difficult, but the multitude of detailed observations following the detection of the gravitational wave event GW170817 has now finally verified these connections.
“The spectrum of the kilonova looked exactly like how theoretical physicists had predicted the outcome of the merger of two neutron stars would appear,” says Levan. “It ties this object to the gravitational wave source beyond all reasonable doubt.”
The infrared spectra taken with Hubble also showed several broad bumps and wiggles that signal the formation of some of the heaviest elements in nature. These observations may help solve another long-standing question in astronomy: the origin of heavy chemical elements, like gold and platinum. In the merger of two neutron stars, the conditions appear just right for their production.
The implications of these observations are immense. As Tanvir explains: “This discovery has opened up a new approach to astronomical research, where we combine information from both electromagnetic light and from gravitational waves. We call this multi-messenger astronomy — but until now it has just been a dream!”
Levan concludes: “Now, astronomers won’t just look at the light from an object, as we’ve done for hundreds of years, but also listen to it. Gravitational waves provide us with complementary information from objects which are very hard to study using only electromagnetic waves. So pairing gravitational waves with electromagnetic radiation will help astronomers understand some of the most extreme events in the Universe.”
UPDATE: THIS EVENT HAS BEEN CANCELED DUE TO CONTINUED AND FORECAST OVERCAST/MOSTLY CLOUDY CONDITIONS.
Stephens Memorial Observatory of Hiram College will be open for public observing Saturday, October 28, from 7:00 to 9:00 PM. That night will feature Hiram’s participation in International Observe the Moon Night, a global event celebrating our nearest neighbor in space. Given good skies, Earth’s Moon will be viewed in spectacular detail via the Observatory’s 1901 telescope. Other objects of interest may also be viewed. Visitors are invited to bring their smart phones or cameras and try lunar photography — it’s harder than you may think!
Cloudy skies at the starting time cancel the event and, in that case, the observatory will not open. No reservations are required and there is no admission fee for observatory public nights.
The Observatory is located on Wakefield Road (Rt. 82) less than a quarter of a mile west of Route 700 in Hiram. There is no parking at the Observatory. Visitors may park on permissible side streets near the Post Office, a short distance east of the observatory.
We hosted our September Open Night as scheduled on the 30th with Earth’s Moon as our primary subject. The sky was (for once) completely clear of clouds and full of stars when we opened the dome for the 9:00 start. In all, 19 folks from small children to senior citizens attended and enjoyed spectacular views of our nearest neighbor in space. Two or three individuals attempted smart phone photography of the Moon with varying degrees of success. We also observed the Andromeda Galaxy and the Perseus Double Cluster. The image above was made just before we closed up and has been corrected for the telescope’s optical “flipping” of the image. Camera used was a Canon EOS 7D equipped with a 50mm lens and held to the telescope’s massive eyepiece. We will look at the Moon again October 28 when we celebrate the annual International Observe the Moon Night. See you then?