Hubble investigates a magnetar’s birthplace
Science & Exploration 15/04/2025 346 views 8 likes Researchers using the NASA/ESA Hubble Space Telescope have discovered that the magnetar SGR 0501+4516 was not born in a neighbouring supernova as previously thought. The birthplace of this object is now unknown, and SGR 0501+4516 is the likeliest candidate in our galaxy for a magnetar that was not born in a supernova. This discovery was made possible by Hubble’s sensitive instruments as well as highly accurate reference data from the European Space Agency's Gaia spacecraft. Artist impression of a magnetar In 2008, NASA’s Swift Observatory spotted brief, intense flashes of gamma rays from the outskirts of the Milky Way. The source, an object named SGR 0501+4516, is one of only about 30 known magnetars in the Milky Way.Magnetars are ultra-dense stellar remnants with extremely strong magnetic fields. They are a special type of neutron star. Neutron stars are some of the most extreme objects in the Universe. These stars typically pack more than the mass of the Sun into a sphere of neutrons about 20 km across. Unsurprisingly, these exotic objects can display several extreme behaviours, such as X-ray and gamma-ray outbursts, intense magnetic fields and rapid rotation.“Magnetars are neutron stars – the dead remnants of stars, composed entirely of neutrons. They’re so heavy and dense that the electrons and protons which make up atoms have been crushed together into neutrons. What makes magnetars unique is their extreme magnetic fields, billions of times stronger than the strongest magnets we have on Earth,” said Ashley Chrimes, lead author of the discovery paper published today in the journal Astronomy & Astrophysics. Ashley is a ESA Research Fellow at the European Space Research and Technology Centre (ESTEC) in the Netherlands. Born from a supernova? Most neutron stars are thought to be born in core-collapse supernovae. These spectacular cosmic explosions happen when stars far more massive than the Sun run out of fuel for nuclear fusion. The star’s outer layers fall inward and rebound off the collapsed core in an explosion that can briefly outshine an entire galaxy. Because magnetars are themselves neutron stars, the natural explanation for their formation is that they too are born in supernovae. This appeared to be the case for SGR 0501+4516, which is located promisingly close to a supernova remnant called HB9. The separation between the magnetar and the center of the supernova remnant on the sky is just 80 arcminutes, or slightly wider than your pinky finger when viewed at the end of your outstretched arm.But a decade-long study with Hubble cast doubt on the magnetar’s birthplace. After initial observations with ground-based telescopes shortly after SGR 0501+4516’s discovery, researchers leveraged Hubble’s exquisite sensitivity and steady pointing to spot the magnetar’s faint infrared glow in 2010, 2012 and 2020. Each of these images was aligned to a reference frame defined by observations from ESA's Gaia mission, which has crafted an extraordinarily precise three-dimensional map of nearly two billion stars in the Milky Way. This method revealed the subtle motion of the magnetar as it inched across the sky. This work therefore demonstrates that Hubble and ESA's Gaia can reveal mysteries never seen before when joining forces.“All of this movement we measure is smaller than a single pixel of a Hubble image,” said co-investigator Joe Lyman of the University of Warwick, United Kingdom. “Being able to robustly perform such measurements really is a testament to the long-term stability of Hubble.”By tracking the magnetar’s position, the team was able to measure the object’s apparent motion across the sky. Both, the speed and direction of SGR 0501+4516’s movement showed that the magnetar could not be associated with the nearby supernova remnant. Tracing the magnetar’s trajectory thousands of years into the past showed that there were no other supernova remnants or massive star clusters that it could be associated with.“This discovery showcases how the all-sky survey of Gaia serves as anchor for very detailed and deep studies with the Hubble observatory," remarks Gaia Project Scientist Johannes Sahlmann. "It is a pleasure to see these two great science missions working together to expand our knowledge of the cosmos." A new pathway for magnetar formation If SGR 0501+4516 was not born in supernova remnant HB9, the magnetar must either be far older than its reported 20 000-year age, or it must have formed in another way. Magnetars may also be able to form through the merger of two lower-mass neutron stars or through a process called accretion-induced collapse. Accretion-induced collapse requires a binary star system containing a white dwarf: the crystallised core of a dead Sun-like star. If the white dwarf ensnares gas from its companion, it can grow too massive to support itself, leading to an explosion – or possibly the creation of a magnetar.“Normally, this scenario leads to the ignition of nuclear reactions, and the white dwarf exploding, leaving nothing behind. But it has been theorised that under certain conditions, the white dwarf can instead collapse into a neutron star. We think this might be how SGR 0501 was born,” added Andrew Levan of Radboud University in the Netherlands and the University of Warwick in the United Kingdom.SGR 0501+4516 is currently the best candidate for a magnetar in our galaxy that may have formed through a merger or accretion-induced collapse. Magnetars that form through accretion-induced collapse could provide an explanation for some of the mysterious cosmic signals called fast radio bursts, which are brief but powerful flashes of radio waves. In particular, this scenario may explain the origin of fast radio bursts that emerge from stellar populations too ancient to have recently birthed stars massive enough to explode as supernovae.“Magnetar birth rates and formation scenarios are among the most pressing questions in high-energy astrophysics, with implications for many of the Universe’s most powerful transient events, such as gamma-ray bursts, superluminous supernovae, and fast radio bursts,” said Nanda Rea of the Institute of Space Sciences in Barcelona, Spain.The research team has further Hubble observations planned to study the origins of other magnetars in the Milky Way, helping to understand how these extreme objects form. The joint ESA/NASA Hubble Space Telescope More informationThe Hubble Space Telescope is a project of international cooperation between ESA and NASA.Release on esahubble.org Contact: ESA Media [email protected]