An international team of astronomers led by the Infrared/Submillimetre Group at the Max Planck Institute for Extraterrestrial Physics (MPE) has announced the discovery of a star so close to Sagittarius A*, the Milky Way’s centrally placed supermassive black hole, that it is experiencing warped spacetime.
With a highly elliptical orbit around Sagittarius A* of only 8.7 years, the newly named S301 comes as close as Saturn does to our Sun during its nearest approach. The research team said this close approach makes it the star with the shortest recorded orbital period and the tightest ever observed in the galaxy’s center.
In a statement emailed to The Debrief, Reinhard Genzel, Director at MPE and Nobel Laureate for Physics in 2020, noted that S301’s historically tight orbit around Sagittarius A* is ten times closer to the Galactic Center than “our previous best star.”
Along with that record, the team said the star’s tight orbit also moves it through a region of space where the black hole’s extreme gravitational pull “drags spacetime itself.”
Genzel noted that “S301 probes spacetime in the Galactic Center,” a phenomenon that astrophysicists believe only occurs in the immediate vicinity of a massive, spinning object like a black hole.
According to the MPE team, the evidence for this warped spacetime shows up in the star’s orbital path. Specifically, they said the star’s path “deviates significantly” from the path predicted by Newton’s classical theory of gravitation.
“This is a clear sign of relativistic effects that occur only in the vicinity of a massive, rotating black hole,” the researchers explained.
To explain the evidence of warped spacetime, the MPE team said two scientific principles are at work. The first, called Schwarzschild Precession, occurs when space itself is curved around a central mass. In the case of S301, the object creating an extended field of warped spacetime around it is the supermassive black hole Sagittarius A*.
“The Schwarzschild solution of general relativity remains a useful approximation to explain the orbit of S2, even for a spinning black hole at the center of the Galaxy,” they explained.
The second relativistic mechanism causing the warped spacetime drag on S301 is called the Lense-Thirring effect. Specifically, the massive black hole exerts a separate force from Schwarzschild Precession due to its rotation.
“A rotating mass, in a sense, drags the surrounding space-time along with it – much like a rotating spoon setting the water in a cup in motion,” the MPE team explained.
Unlike the more powerful effect of gravity, the team said the effect on the star caused by the rotation of Sagittarius A* is “significantly weaker and therefore more difficult to detect.” This rarity marks the team’s observation of the effect, another historic first.
“S301 is the first star to orbit directly in the region around Sagittarius A* where the frame-dragging effect is extreme,” explained Felix Mang, PhD student at MPE and corresponding author of the study. “We’re not just measuring spacetime curvature; we are measuring how it gets distorted by the rotation of the black hole itself. That is unique.”
Astronomers first identified S301 in spring 2023 using the GRAVITY instrument at the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO) in Chile. Unlike conventional observatories, GRAVITY observes targets simultaneously with four 8-meter telescopes. The light is then combined into a single image, resulting in an angular resolution 40 times sharper than images captured by a single telescope.
“GRAVITY’s exceptional resolution makes it possible to observe stars at the center of the Milky Way on scales comparable to the size of our solar system, even when they are extremely faint,” the MPE team explained, adding that “this unprecedented combination of precision and sensitivity has made it possible to detect S301, a new and extremely faint star.”
When discussing the next steps in the investigation of the star experiencing warped spacetime, the MPE team noted that a recent upgrade to the facility, GRAVITY+, which includes a new adaptive optics system and laser guide stars, “has increased the instrument’s sensitivity by a factor of 10 to 100.” Genzel said the upgrade will lead to even more discoveries in a relatively short time.
“Within the next decade, we will measure the black hole’s rotation directly — a milestone for general relativity,” The researcher explained.
Frank Eisenhauer, director at MPE and Principal Investigator of the GRAVITY and GRAVITY+ projects, said the opportunity to discover “the beauty of nature” in the form of S301 “is truly a dream come true.” The researcher also pointed to future observations and the new tools that will make them possible, while seemingly harkening back to a popular 1960s TV show introduction championing the exploration of space.
“GRAVITY+ and the upcoming MICADO instrument, currently being developed in an international consortium led by MPE for the ESO Extremely Large Telescope [will help us] to explore strange new worlds, seek out new physics, and see what nobody has seen before.”
The study “Discovery of a star sensitive to the spin of Sagittarius A*” was published in Nature.
Christopher Plain is a Science Fiction and Fantasy novelist and has spent the last six years as Associate News Editor and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him at christopher@thedebrief.org.
The German eROSITA Consortium (eROSITA-DE), led by the Max Planck Institute for Extraterrestrial Physics (MPE), has completed the most comprehensive census of the high-energy universe ever assembled.
Released as eROSITA Data Release 2 (DR2), the new high-energy universe catalog includes nearly two million X-ray sources, essentially doubling the number cataloged in DR1. The team behind the achievement said the new catalog, which has been made available to the wider scientific community, marks a “major step forward” in mapping the entire high-energy universe.
“DR2 is the best inventory of the X-ray sky we have to date and opens the door to robust statistical studies of cosmic populations,” explained Miriam E. Ramos-Ceja, Ground Segment Manager of the eROSITA instrument and lead author of the DR2 publication.
DR2 was built from the first three scans captured by the eROSITA telescope during the Spectrum-Roentgen-Gamma (SRG) mission. According to a statement emailed to The Debrief, the new high-energy map combined data from multiple passes over the sky, significantly increasing the instrument’s survey depth.
After beginning its mission in December 2019, the observatory surveyed the entire sky every six months. This mission length increased the scans’ depth and sensitivity. The new DR2 includes data captured during the mission’s first 556 days. MPE scientists said the final catalog comprises three “full sky surveys.”
“By stacking these observations, the survey reaches significantly fainter fluxes than the first release, enabling the large increase in detected sources,” they explained.
The approach also revealed a large population of previously uncatalogued systems.
For example, the DR2 catalog includes nearly two million X-ray sources detected in the 0.2–2.3 keV band. The survey also revealed over 1.9 million “point-like sources.” The team said these detections are “primarily stars and actively accreting supermassive black holes.” The survey also added around 64,000 extended sources, including newly cataloged galaxy clusters, nearby galaxies, and supernova remnants.
Along with the primary catalog, the new release includes a complementary “hard-band” catalog that includes 15,000 sources detected at higher energies (2.3–5.0 keV). The team said these detections revealed “heavily obscured and intrinsically energetic systems” that scans performed at ‘softer’ X-ray energies typically overlook.
“Together, these catalogues capture the full diversity of the X-ray sky, from nearby stellar coronae to distant supermassive black holes and massive galaxy clusters,” the team explained, adding that many of the cataloged objects are newly identified in X-rays, while others “can now be studied with substantially improved precision.”
Although more analysis is needed to accurately characterize every high-energy source discovered by the new survey, the team said the DR2 includes “multi-wavelength information” that associates the newly cataloged X-ray detections with their most likely optical and infrared counterparts.
“X-ray detection is only the first step,” explains Mara Salvato, eROSITA spokesperson and chair of the follow-up working group. “By linking X-ray sources to their counterparts at other wavelengths, we can work out what these objects are, where they sit on the cosmic distance ladder, and build clean, well-defined samples on an unprecedented scale.”
This data suggests that approximately 88% of the newly discovered sources come from outside the Milky Way Galaxy. The team said the new sources are “dominated by accreting supermassive black holes.”
When discussing the significance of the new DR2 high-energy catalog, the team highlighted its coincidental release with the latest Sloan Digital Sky Survey (SDSS).
“By combining SDSS spectroscopy with eROSITA’s X-ray data, researchers can build three-dimensional maps of active black holes across the sky, revealing how these rapidly growing objects are distributed and evolve across cosmic time,” they explained.
For example, combining eROSITA’s X-ray catalog with the SDSS spectroscopic and photometric redshift data has already resulted in what the team described as “one of the largest and most detailed studies of accreting supermassive black holes to date.” The researchers said these “elusive objects” formed surprisingly early in the history of the Universe, so capturing new data of their growth at high redshift is invaluable.
“The most luminous black holes at high redshift are like needles in a haystack,” explained the corresponding study’s lead author, William Roster. “Thanks to DR2 we found more needles than expected, suggesting that rapidly growing black holes were more abundant in the early Universe than previously thought”
Due to a pre-existing agreement between the German and Russian eROSITA consortia, the new DR2 covers the western Galactic hemisphere. However, the researchers note, within this region of the sky, the new catalog “represents the largest and most homogeneous public X-ray dataset currently available.”
eROSITA Principal Investigator Andrea Merloni said the new dataset of unprecedented scale and completeness has been made available to the global astronomical community. MPE Director Kirpal Nandra agreed, adding that the MPE team hopes the most complete catalog of high-energy sources ever assembled will provide “a unique foundation for discoveries ranging from rare objects to large-scale population studies.”
“eROSITA just set another world record in terms of X-ray source numbers – and it won’t be the last,” Merloni concluded.
The eROSITA-DE DR2 catalogs, upper-flux-limit server, and full documentation are publicly accessible via the eROSITA-DE Science Data Archive.
Christopher Plain is a Science Fiction and Fantasy novelist and has spent the last six years as Associate News Editor and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him at christopher@thedebrief.org
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