The discovery of low-level ripples throughout the universe called the gravitational wave background has set physicists looking for exotic explanations.

By Alex Wilkins

Dr. Varsha Ramachandran from the Center for Astronomy of Heidelberg University (ZAH) and her colleagues uncovered the first “stripped” star of intermediate-mass. This discovery marks a missing link in our picture of stellar evolution toward systems with merging neutron stars, which are crucial to our understanding of the origin of heavy elements, such as silver and gold. Dr. Ramachandran is a postdoc in the research group of Dr. Andreas Sander, located at ZAH’s Astronomisches Rechen-Institut (ARI). These results were now published in Astronomy & Astrophysics.

The team of researchers discovered the first representative of the long-predicted, but as yet unconfirmed population of intermediate-mass stripped stars. “Stripped stars” are stars that have lost most of their outer layers, revealing their hot and dense helium-rich core, which results from the nuclear fusion of hydrogen to helium. Most of these stripped stars are formed in binary star systems in which one star’s strong gravitational pull peels off and accretes matter from its companion.

For a long time, astrophysicists have known of low-mass stripped stars, known as subdwarfs, as well as their massive cousins, known as Wolf-Rayet stars. But until now, they have never been able to find any of the so-called “intermediate-mass stripped stars,” raising questions whether our basic theoretical picture needs a major revision.

The announcement last week of the discovery of the gravitational wave background has rocked astronomy, but work has already begun on how this new window to the universe can be used to tease apart how the universe works.

At this week’s National Astronomy Meeting 2023 at Cardiff University in Wales, UK, an international team of cosmologists revealed that observations of gravitational waves from merging black holes may reveal the true nature of “dark matter.”

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Observations of gravitational waves from merging black holes—and their absence—may unveil the true nature of dark matter, according to new research.

Subtle shifts in stellar signals reveal pervasive waves from mergers of giant black holes.

A team of astronomers led by researchers from the University of Birmingham, University College London and Queen’s University Belfast have discovered one of the most dramatic ‘switches on’ of a black hole ever seen. They will present their findings on Tuesday 4 July at the 2023 National Astronomy Meeting in Cardiff. The work will also be published in Monthly Notices of the Royal Astronomical Society.

J221951-484240, known as J221951, is one of the most luminous transients—astrophysical objects that change their brightness over a short period of time—ever recorded. It was discovered by Dr. Samantha Oates, an astronomer at the University of Birmingham, and her team, in September 2019 while searching for the electromagnetic light from a gravitational wave event. The team were using the Ultra-Violet and Optical Telescope on board the Neil Gehrels Swift Observatory to look for a kilonova, the sign of a neutron star merging with another neutron star or a black hole. A kilonova typically appears blue, then fades and turns more red in color over a timescale of days. What they found instead something even more unusual: J221951. The transient appeared blue, but didn’t change color or fade rapidly as a kilonova would.

Multiple telescopes were used to follow-up J221951 and determine its nature, including NASA’s Swift/UVOT and Hubble Space Telescope, the South African Large Telescope, and ESO facilities such as the Very Large Telescope and the GROND instrument on the MPG/ESO 2.2-meter telescope at the La Silla Observatory.

Scientists have for the first time observed the early universe running in extreme slow motion, unlocking one of the mysteries of Einstein’s expanding universe. The research is published in Nature Astronomy.

Einstein’s general theory of relativity means that we should observe the distant—and hence ancient— universe running much slower than the present day. However, peering back that far in time has proven elusive. Scientists have now cracked that mystery by using quasars as “clocks.”

“Looking back to a time when the universe was just over a billion years old, we see time appearing to flow five times slower,” said lead author of the study, Professor Geraint Lewis from the School of Physics and Sydney Institute for Astronomy at the University of Sydney.

This thrum of gravitational waves is constantly pulsing through the universe. It opens a window into the earliest moments after the Big Bang.