Astronomers spot bright flashes from a mysterious new class of cosmic object

CNN

6 days ago

Astronomers have detected an astonishing celestial object emitting bright flashes of radio waves and X-rays that last for two minutes and repeat every 44 minutes.
In a fresh twist, the discovery marks the first time powerful X-rays have been associated with an object that might be a long-period transient. Astronomers first spotted this cryptic new class of objects in 2022, and fewer than a dozen have been found so far.
'Long-period (radio) transients (LPTs) are a recently identified class of cosmic objects that emit bright flashes of radio waves every few minutes to several hours,' said Dr. Andy Wang, an associate lecturer at the Curtin Institute of Radio Astronomy in Australia, in an email. 'What these objects are, and how they generate their unusual signals, remain a mystery.'
The object, named ASKAP J1832-0911, is located about 15,000 light-years from Earth in the same galaxy as our solar system.
The X-ray emissions, uncovered by NASA's Chandra X-ray Observatory, could be the key to helping astronomers understand more about the true nature of these intriguing cosmic objects and their pulsing behavior.
'X-rays usually come from extremely hot and energetic environments, so their presence suggests that something dramatic happened to the object,' said Wang, lead author of a study reporting the observations, which was published Wednesday in the journal Nature.
The long-period transients appear to be more energetic than previously believed if they can produce X-rays, which have more energy than radio waves, Wang said.
Now, researchers are trying to figure out the source of ASKAP J1832-0911's radio waves and X-rays, which don't fit into a neat box for categorization, and whether it's truly representative of a long-period transient or an eccentric outlier.
At first, the team thought the object might be a magnetar, or the dense remnant of a star with an extremely powerful magnetic field, or a pair of stars that includes a highly magnetized dead star called a white dwarf. But neither of those quite matched up with the bright and variable emissions of radio waves and X-rays, the researchers said.
'This object is unlike anything we have seen before,' Wang said. 'Even those theories do not fully explain what we are observing. This discovery could indicate a new type of physics or new models of stellar evolution.'
Astronomers traced a previous detection of a long-period transient, announced in March, to a white dwarf that's closely orbiting a small, cool red dwarf star. The two stars orbit each other so closely that their magnetic fields interact, emitting long radio bursts.
In that study, researchers detected signals in visible and infrared light that corresponded with the signals they observed, suggesting they could belong to two different types of objects. Wang's team made no such observations of ASKAP J1832-0911, he said.
Charlie Kilpatrick, coauthor of the March study, called the new find 'exciting.' He did not participate in the new research.
'The nature of this source bridges the gap between the most extreme magnetars and white dwarfs, which is telling us just how extreme (these) compact objects can be,' wrote Kilpatrick, research assistant professor at Northwestern University's Center for Interdisciplinary Exploration and Research in Astrophysics in Illinois, in an email.
Wang said future X-ray observations may reveal more about the object, such as its temperature and size, which researchers could use to determine the source. But the new detections are already changing the way Wang and his collaborators think about long-period transient signals.
Radio astronomers regularly scan the sky using the Australian Square Kilometre Array Pathfinder, or ASKAP, located in Wajarri Yamaji Country in Western Australia and operated by Australia's Commonwealth Scientific and Industrial Research Organization, or CSIRO.
Wang and his collaborators first picked up on a bright signal from the object in December 2023. Then, the object released extremely bright pulses of radio waves in February 2024. Fewer than 30 known objects in the sky have ever reached such brightness in radio waves, Wang said.
By coincidence, the Chandra X-ray Observatory was pointing at something else, but it happened to catch X-ray observations of the 'crazy' bright phase of the long-period transient, Wang said.
'Discovering that ASKAP J1832-0911 was emitting X-rays felt like finding a needle in a haystack,' Wang said. 'The ASKAP radio telescope has a wide field view of the night sky, while Chandra observes only a fraction of it. So, it was fortunate that Chandra observed the same area of the night sky at the same time.'
Unlike rapidly spinning neutron stars called pulsars, which release pulses that last milliseconds to seconds, ASKAP J1832-0911 periodically varied in radio wave and X-ray intensity every 44 minutes. The object also dropped off in X-ray and radio wave intensity. Observations taken by Chandra six months later in August 2024 showed no X-rays.
The team also used the CRACO, or Coherent Radio Astronomy Core, instrument, which was recently developed to detect mysterious fast radio bursts, or millisecond-long flashes of radio waves, and other celestial phenomena. The instrument can rapidly scan and process data to spot bursts and zero in on their location.
'That's the equivalent of sifting through a whole beach of sand to look for a single five-cent coin every minute,' said Dr. Keith Bannister, a CSIRO astronomer and engineer who helped develop the instrument.
But CRACO is also able to detect long radio pulses and helped the team determine that the bursts of radio waves were repeating. Other observations showed that the X-rays were repeating as well.
Data from telescopes in the United States, South Africa and India and collaborators from around the world made the extremely rare detection a truly global effort, Wang said.
Moving forward, Wang and his team will continue searching for more objects emitting these long radio pulses.
'Finding one such object hints at the existence of many more,' said study coauthor Dr. Nanda Rea, a professor at the Institute of Space Science and The Institute of Space Studies of Catalonia in Spain, in a statement. 'The discovery of its transient X-ray emission opens fresh insights into their mysterious nature.'