Lumbing X-rays astonish astronomers after years of landmark neutron star collisions

New, most complete start-to-finish view Neutron star Merger scientists rewrite the way scientists understand these phenomena.

It has been three years since the discovery of the neutron star merger Gravitational waves. And since that day, an international team of researchers led by astronomer Eleanor Troja of the University of Maryland has been constantly monitoring subsequent radiation emissions to provide the most complete picture of such an event.

Their analysis provides potential specifications for X-rays that continued to spread from the collision after the models predicted they would close. The study also found that important information is missing in current models of neutron stars and compact body collisions. The research was published in the journal October 12, 2020 Monthly instructions of the Royal Astronomical Society.

“We are entering a new phase for our understanding of neutron stars,” said Troja, an associate research scientist at the UMD’s astronomy department and lead author of the paper. “We don’t really know what to expect beyond this point, as not all of our models were predicting any X-rays and 1,000 days after the collision we were surprised to see them. It may take years to find the answer to what is happening, but our research opens the door to many possibilities.

The neutron star merger studied by the Trojan team – GW170817 – was first identified by the gravitational waves found on August 17, 2017 by the Gravity-Wave Observatory and its equivalent Virgo. Explosive rays and light. It was the first and only time that astronomers were able to observe the radiation associated with gravitational waves, although they have long known that such radiation occurs. All the other gravitational waves observed to date have arisen from very weak and very distant events to detect radiation from the earth.

Seconds after the discovery of GW170817, scientists noticed an early jet of energy known as a gamma ray explosion, then a slow kilonova, a cloud of gas that erupted behind the initial jet. The light from Kilonova lasted for about three weeks and then faded. Meanwhile, nine days after the gravitational wave first met, the telescope observed something they had not seen before: an X-ray. Delo, a scientist based on well-known astrophysics models, predicted that the initial jet from the collision of a neutron star would move into interstellar space, creating its own shockwave, emitting X-rays, radio waves and light. This is known as nephrolo. But such a later death had never been seen before. In this state, the glow peaked 160 days after the gravitational waves were found and then quickly faded. But X-rays remained. They were last observed by the Lunar X-Ray Observatory two and a half years after GW 170817 was first discovered.

The new research paper suggests some possible explanations for long-term X-ray emissions. One possibility is that these X-rays introduce a whole new feature of post-collision motion, and the dynamics of the explosion of gamma rays are suddenly different than expected.

“We have collided so close that it is visible that a window opens into the whole process that we can hardly access,” said Troja, who is also a research scientist. NASAOf Goddard Space Flight Center. “It may be that there are physical processes that we have not incorporated into our models because when they form planes we are not already consistent in the phase with which we are more familiar.”

Another possibility is that the expansion of the gas cloud behind Kilonova and the initial jet of radiation could create their own shock wave that took longer to reach Earth.

“We saw Kilonova, so we know this is a gas cloud, and X-rays from its shock wave can only reach us,” said Geoffrey Ryan, a postdoctoral fellow at the UMD department of astronomy and its co-author. Learning. “But if we need more data to understand what we are seeing. If it is, it can give us a new tool, the signature of these events that we did not recognize before. It can help us detect neutron star collisions in previous records of X-ray radiation. “

The third possibility is that something may have been left behind after the collision, probably the remnants of an X-ray out of a neutra star.

Further analysis is needed before researchers can confirm exactly where the delayed X-rays came from. Some answers may come in December 2020, when the telescopes will once again be built with the source of GW 170817 in mind. (The last observation was in February 2020.)

“This could be the final breath of a historical source or the beginning of a new story, in which the signal in the future shines again and it may appear for decades or even centuries,” Troja said. “Whatever happens, what we know about this event could rewrite the Neutron Star merger and our models is changing.”

Reference: “One thousand days after the merger: Continuous X-ray emission from GW170817” E. Troja, H. Van Irten, b. Zhang, g. Ryan, L. Piro, R. Ricky, b. O’Connor, by M. H. Viringa, S.B. Senko and T. Sakamoto, 12 October October 122020, Monthly instructions of the Royal Astronomical Society.
DOI: 10.1093 / MNRS / STA 2626

Additional authors of the UMD Department of Astronomy paper are Faculty Assistant Brendan O’Connor and Adjutant Associate Professor Stephen Senko.

The work was partially supported by NASA (Lunar Award Number, G0920071A, NNX16AB66G, NNX17AB18G, and 80NSSC20K0389.), Joint Space-Institute Institute Prize Postdoctoral Fellowship, and European Union Horizon 20205 (Award). The content of this article does not necessarily reflect the views of these organizations.