Astronomers find a golden glow in a distant stellar collision


On August 17, 2017, scientists marked the story with the first direct observation of a merger between two neutron stars.

It was the first cosmic event detected by both gravitational waves and the entire spectrum of light, from gamma rays to radio broadcasts.

The impact also created a kilonova – a supercharged blast that instantly forged gold and platinum for several hundred planets. The observations provided the first convincing proof that kilonovae produce large quantities of heavy metals, a result long predicted by the theory. Astronomers suspect that all of the gold and platinum on Earth has formed as a result of ancient kilonovae created during neutron star collisions.

On the basis of the 2017 event data, first spotted by the Laser Interferometer Gravitational Wave Observatory (LIGO), astronomers began to adjust their assumptions about how a kilonova should appear to observers related to the Earth. A team led by Eleonora Troja, an associate researcher at the Department of Astronomy at the University of Maryland, has re-examined data from a gamma-ray spurt spotted in August 2016 and found new evidence of the effects. a kilonova that went unnoticed during the first observations.

The NASA Neil Gehrels Swift Observatory began tracking the 2016 event, named GRB160821B, minutes after its detection. The first captures allowed the research team to gather new information that was missing in Kilonova's observations on the LIGO event, which only started about 12 hours after the initial collision. Troja and his colleagues reported these new discoveries in the review Avis of the Royal Astronomical Society of August 27, 2019.

"The 2016 event was very exciting at first, it was visible and visible with all the big telescopes, including NASA's Hubble Space Telescope, but that was not what we expected – we expected the infrared emission gets brighter and brighter for weeks, "said Troja, who also has a meeting at NASA's Goddard Space Flight Center. "Ten days after the event, there was almost no signal left, we were all so disappointed, and a year later the LIGO event happened." We reviewed our old data. with a new look and realized that we had actually caught a kilonova in 2016. The infrared data for both events have similar brightness and an identical time scale. "

The similarities between the two events suggest that the 2016 kilonova also resulted from the fusion of two neutron stars. Kilonovae may also result from the fusion of a black hole and a neutron star, but it is unclear whether such an event would produce a different signature for X-ray, infrared, radio and optical observations.

According to Troja, the information gathered at the 2016 event does not contain as much detail as the sightings of the LIGO event. But the cover of those early hours – which did not feature in the LIGO event report – revealed important new information about the early stages of the kilonova. For example, the team had a first look at the new object remaining after the collision, which was not visible in the LIGO event data.

"The rest could be a highly magnetized hypermassive neutron star, known as the magnetar, which survived the collision and then collapsed into a black hole," said Geoffrey Ryan, postdoctoral fellow of the UMD Prize. Joint Space-Science Institute (UMD). of Astronomy and co-author of the research paper. "It's interesting, because the theory suggests that a magnetar should slow or even stop the production of heavy metals, the ultimate source of the infrared signature of a kilonova.Our analysis suggests that heavy metals are able to escape the thirst-quenching influence of the remaining object. "

Troja and his colleagues plan to apply lessons learned to re-evaluate past events, while improving their approach to future observations. A number of candidate events have been identified with optical light observations, but Troja is more interested in events with a strong infrared light signature – the indicator indicator of heavy metal production.

"The very powerful infrared signal of this event makes it the clearest kilonova we have seen in the far universe," Troja said. "I am very interested in how the properties of kilonova change with different spawners and final remains.On observing more and more of these events, we can learn that there are many types of kilonovae in the same family, as in the case of many types of supernovae, it's so exciting to shape our knowledge in real time. "

The research paper, "Remanence and Kilonova Short Film GRB 160821B", Eleonora Troja, Alberto Castro-Tirado, Josefa Becerra Gonzalez, Youdong Hu, Geoffrey Ryan, S. Bradley Cenko, Roberto Ricci, Giovanni Novara, Ruben Sanchez- Rámirez, José Acosta-Pulido, Kendall Ackley, Maria Caballero García, Stephen Eikenberry, Sergiy Guziy, Seob Jeong, Amy Lien, Isabel Márquez, Isabel Márquez, Sashi Pandey, Ii Park, Takanori Sakamoto, Juan Tello, Igor Sokolov, Vladimir Sokolov , Andrea Tangier, Bin Bin Zhang, Sylvain Veilleux, was published in the review Avis of the Royal Astronomical Society of August 27, 2019.

This work was supported by the National Science Foundation (Award No. AST-1005313); Spanish Ministry of Science, Innovation and Universities (price No. SEV-2017-0709); the Italian Space Agency (prices nos 2015-046-R.0 and 2017-14-H.0); the Horizon 2020 Framework Program of the European Union (award 654215); and the China Scholarships Council (Decision No. 201406660015). The content of this article does not necessarily reflect the views of these organizations.

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