Texas Tech University

Neutron Star Cosmic Fireworks Shed Light on Old Black Hole Mystery

Doug Hensley

March 2, 2023

Alexandra Tetarenko

Texas Tech researcher Alexandra Tetarenko is part of an international team that discovered never before seen behavior from a neutron star system.

Texas Tech University's Alexandra Tetarenko, a NASA Einstein Fellow, is among an international scientific team that discovered a neutron star that consumed matter in a manner previously only observed in black holes. The group's discovery has helped identify key new ingredients needed to explain the behavior of matter near these astrophysical objects. Their findings were published Wednesday (March 1) in the journal Nature

“While I typically spend most of my time thinking about black holes, it has been incredibly exciting to be a part of this team of brilliant astronomers,” said Tetarenko, who came to Texas Tech's Department of Physics and Astronomy in the fall of 2021 as part of the NASA Hubble Fellowship Program (NHFP). 

Tatarenko's research focuses on studying relativistic jets, beams of energetic material accelerated close to the speed of light that are launched from compact objects in our galaxy.

“We have been able to use our black hole knowledge as a template to understand the behavior of a completely different type of explosive compact object,” she said.

X-ray binaries are systems formed by a compact object like a neutron star or black hole that is gravitationally paired with a star of similar size to our Sun. The compact object swallows matter from its companion star through a disk that emits large amounts of light, especially in X-rays. The process in which the compact object attracts matter, known as accretion, usually occurs in violent eruptions during which the system becomes up to 1,000 times brighter. Part of the material that spirals down toward the compact object also can be ejected back into space through powerful outflows, which emit light at longer radio and infrared wavelengths.

The target object of this study, X-ray binary Swift J1858.6-0814, was discovered in 2018 during one of these spectacular eruptive episodes, and had baffled the astronomical community since the earliest observations. The system showed incredibly rapid increases in brightness, known as flares, over the timescales of a year, emitting all different types of light from radio waves to X-rays. The origin of these "cosmic fireworks" was unknown, but they were so bright that the scientific community believed the compact object must be a black hole. However, the discovery of thermonuclear explosions from Swift J1858, which can only occur on the solid surface of a compact object, confirmed that Swift J1858 must contain a neutron star instead.

Thanks to an international observing campaign, consisting of five different ground and space-based telescopes, Tetarenko and the team of astronomers discovered this object exhibits the same exotic accretion behavior (known as accretion instabilities) as a well-studied galactic black hole system (GRS 1915+105), and thus they could use this black hole as a Rosetta stone for decoding the complex behavior of this particular neutron star.

"This study demonstrates that such an ‘instability' is a fundamental physical process, independent of the nature of the compact object, and in turn presents a new scenario that allows us to explain what happens in the vicinity of these exotic objects when they consume matter at very high rates,", said Federico Vincentelli, lead researcher on the article.

With a view to future research, the recent discovery provides the scientific community with new ingredients to understand the origin of accretionary instabilities. Vincentelli, Tetarenko and the rest of the team now plan to extend this study to other very luminous systems to continue to understand more about these astrophysical phenomena.