Astronomers have detected the presence of a rare star with a powerful magnetic field in a neighboring galaxy after it suddenly emitted an extremely brief burst of energy. This star, identified as a magnetar, is one of the few known stars of its kind and the first of its kind confirmed to exist outside of our Milky Way galaxy.
The European Space Agency announced in a press release on April 24 that astronomers at the agency observed a burst of highly energetic gamma rays from the nearby Cigar Galaxy in November 2023, lasting only a tenth of a second.
Also known as the M82 galaxy, the Cigar Galaxy is located in the Ursa Major constellation and is approximately 12 million light-years away from Earth. It is a bright galaxy known for hosting numerous actively forming stars.
Following the gamma-ray burst, astronomers monitored the galaxy using multiple ground-based telescopes but did not detect any signals in X-rays or visible light, and gravitational waves were not detected by instruments on Earth.
The astronomers explained that gamma-ray bursts, the most energetic explosions in the universe, typically originate from distant galaxies, but this particular burst originated from a bright neighboring galaxy. The absence of gradually fading X-ray sources typically associated with gamma-ray bursts led them to conclude that this signal came from a magnetar in the Cigar Galaxy, rather than a conventional gamma-ray burst.
When a star with a mass greater than eight times that of the Sun reaches the end of its life, it undergoes a supernova explosion, leaving behind either a black hole or a neutron star. Neutron stars are incredibly dense stellar remnants with masses exceeding that of the Sun but compressed into a size comparable to a city. They rotate rapidly and possess strong magnetic fields.
Ashley Chrimes, a researcher at the European Space Agency, remarked, “Some young neutron stars exhibit extremely strong magnetic fields, surpassing those of typical neutron stars by up to 10,000 times. These are known as magnetars and emit bursts of energy in a flashing manner, sometimes of immense magnitude.”
Despite over 50 years of observing gamma-ray bursts, scientists have only witnessed massive bursts from magnetars in our galaxy three times, with one instance detected in December 2004 originating from 30,000 light-years away but still capable of affecting Earth’s upper atmosphere, akin to how solar flares impact our planet.
The lead author of the study and astrophysicist at the National Institute for Astrophysics in Italy, Sandro Mereghetti, highlighted that this recent detection of a flash confirmed for the first time the existence of magnetars outside of our galaxy. They suspect that certain previously detected gamma-ray bursts may also have stemmed from massive flashes of magnetars.
Chrimes noted that this discovery opens up avenues for exploring other massive magnetars. “By identifying more magnetars, we can begin to understand how often these flashes occur and how these stars lose energy during this process.”
The discovery of a magnetar in the Cigar Galaxy indicates that these stars are likely young neutron stars. Researchers plan to search for more magnetars in regions where other stars are forming to gain further insights into these unique celestial bodies.
The findings of this study were published in the journal Nature on April 24.