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Hubble investigates SGR 0501+4516 and the magnetar’s birthplace

By ScientifiCult 15 April 2025

Hubble investigates SGR 0501+4516 and the magnetar’s birthplace

Magnetars are ultra-dense stellar remnants with extremely strong magnetic fields. 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 precise benchmarks from ESA’s Gaia spacecraft.

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.

A magnetar is 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 kilometres 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. Chrimes is a European Space Agency Research Fellow at the European Space Research and Technology Centre (ESTEC) in the Netherlands.

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 the European Space Agency’s Gaia spacecraft, 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.

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.

At the centre of the image, there is a very bright white-blueish ball, representing the neutron star, with white/blue filaments streaming out from its polar regions, representing magnetic field lines. Some filaments loop around the centre ball, connecting the magnetic north pole to the south. Two blueish beams stream out the two opposite poles towards space. The deep blue background depicting deep space is dotted with small bright-white spots symbolising stars. — This is an artist’s impression of a magnetar, which is 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 kilometres 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 a specific type of neutron star that are distinguished by their exceptionally strong magnetic fields (which are significantly stronger than those of typical neutron stars).
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. It is one of only about 30 known magnetars in the Milky Way.
Credit: ESA

Bibliographic information:

The infrared counterpart and proper motion of magnetar SGR 0501+4516, Astronomy & Astrophysics Volume 696, April 2025 A127, DOI: https://doi.org/10.1051/0004-6361/202453479

Press release from ESA Hubble.

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Astronomy

GRB 230307A: heavy element tellurium detected from a kilonova

By ScientifiCult 25 October 2023

JWST detected the neutron star merger (kilonova) that generated the explosion that created GRB 230307A and helped detecting the heavy element tellurium

Webb’s study of the second-brightest gamma-ray burst ever seen reveals tellurium.

Under what conditions many chemical elements are created in the universe has long been shrouded in mystery. This includes elements that are highly valuable, or even vital to life as we know it. Astronomers are now one step closer to an answer thanks to the James Webb Space Telescope and a high-energy event: the second-brightest gamma-ray burst ever detected, most likely caused by the merging of two neutron stars—which resulted in an explosion known as a kilonova. Using Webb’s spectacular sensitivity, scientists captured the first mid-infrared spectrum from space of a kilonova, which marked Webb’s first direct look at an individual heavy element from such an event.

Bright galaxies and other light sources in various sizes and shapes are scattered across a black swath of space: small points, hazy elliptical-like smudges with halos, and spiral-shaped blobs. The objects vary in colour: white, blue-white, yellow-white, and orange-red. Toward the centre right is a blue-white spiral galaxy seen face-on that is larger than the other light sources in the image. The galaxy is labelled “former home galaxy.” Toward the upper left is a small red point, which has a white circle around it and is labelled “GRB 230307A kilonova. — A team of scientists has used the NASA/ESA/CSA James Webb Space Telescope to observe an exceptionally bright gamma-ray burst, GRB 230307A, and its associated kilonova. Kilonovas—an explosion produced by a neutron star merging with either a black hole or with another neutron star—are extremely rare, making it difficult to observe these events. The highly sensitive infrared capabilities of Webb helped scientists identify the home address of the two neutron stars that created the kilonova.
This image from Webb’s NIRCam (Near-Infrared Camera) instrument highlights GRB 230307A’s kilonova and its former home galaxy among their local environment of other galaxies and foreground stars. The neutron stars were kicked out of their home galaxy and travelled the distance of about 120,000 light-years, approximately the diameter of the Milky Way galaxy, before finally merging several hundred million years later.
This image is a composite of separate exposures acquired by the James Webb Space Telescope using the NIRCam instrument. Several filters were used to sample wide wavelength ranges. The colour results from assigning different hues (colours) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colours are: Blue: F115W + F150W Green: F277W Red: F356W + F444W
Credit: NASA, ESA, CSA, STScI, A. Levan (IMAPP, Warw), A. Pagan (STScI)

A team of scientists has used multiple space- and ground-based telescopes, including the NASA/ESA/CSA James Webb Space Telescope, to observe an exceptionally bright gamma-ray burst, GRB 230307A, and identify the neutron star merger that generated the explosion that created the burst. Webb also helped scientists detect the chemical element tellurium in the aftermath of the explosion.

Other elements near tellurium on the periodic table — like iodine, which is needed for much of life on Earth — are also likely to be present among the kilonova’s ejected material. A kilonova is an explosion produced by a neutron star merging with either a black hole or with another neutron star.

“Just over 150 years since Dmitri Mendeleev wrote down the periodic table of elements, we are now finally in a position to start filling in those last blanks of understanding where everything was made, thanks to Webb,”

said Andrew Levan of Radboud University in the Netherlands and the University of Warwick in the United Kingdom, lead author of the study.

While neutron star mergers have long been theorised as being the ideal “pressure cookers” to create some of the rarer elements substantially heavier than iron, astronomers have previously encountered a few obstacles to obtaining solid evidence.

The spectrum is plotted as a line graph of brightness versus wavelength of light (microns). The spectral lines range in wavelength of light along the x-axis, with the first tic labelled as “1.0” and the last tic labelled as “5.0,” and in brightness, with the level of brightness becoming greater moving higher along the y-axis. The Webb spectral line is white and jagged. About a third of the way across the graph, there is a distinct peak between 2.0 and 2.5 microns. After 2.5 microns, the spectral line slopes gradually up to the right. The model spectral line is red and smoother than the Webb data. The model’s spectral line at 1.0 micron begins low (dim) and flat before peaking between 2.0 and 2.5 microns, similar to the Webb data. The area below the model spectral line is shaded red and labelled “Tellurium T E.” The model spectral line then descends after 2.5 microns and follows the general trend of the Webb data. — This graphic presentation compares the spectral data of GRB 230307A’s kilonova as observed by the James Webb Space Telescope and a kilonova model. Both show a distinct peak in the region of the spectrum associated with tellurium, with the area shaded in red. The detection of tellurium, which is rarer than platinum on Earth, marks Webb’s first direct look at an individual heavy element from a kilonova.
Though astronomers have theorised neutron star mergers to be the ideal environment to create chemical elements, including some that are essential to life, these explosive events—known as kilonovas—are rare and rapid. Webb’s NIRSpec (Near-Infrared Spectrograph) acquired a spectrum of GRB 230307A’s kilonova, helping scientists secure evidence of the synthesis of heavy elements from neutron star mergers.
With Webb’s extraordinary ability to look further into space than ever before, astronomers expect to find even more kilonovas and acquire further evidence of heavy element creation.
Credit: NASA, ESA, CSA, J. Olmsted (STScI)

Kilonovas are extremely rare, making it difficult to observe these events. Short gamma-ray bursts (GRBs), traditionally thought to be those that last less than two seconds, can be byproducts of these infrequent merger episodes. In contrast, long gamma-ray bursts may last several minutes and are usually associated with the explosive death of a massive star.

The case of GRB 230307A is particularly remarkable. First detected by NASA’s Fermi Gamma-ray Space Telescope in March, it is the second brightest GRB observed in over 50 years of observations, about 1000 times brighter than a typical gamma-ray burst that Fermi observes. It also lasted for 200 seconds, placing it firmly in the category of long-duration gamma-ray bursts, despite its different origin.

“This burst is way into the long category. It’s not near the border. But it seems to be coming from a merging neutron star,”

added Eric Burns, a co-author of the paper and member of the Fermi team at Louisiana State University.

The collaboration of many telescopes on the ground and in space allowed scientists to piece together a wealth of information about this event as soon as the burst was detected. It is an example of how satellites and telescopes work together to witness changes in the Universe as they unfold.

After the initial detection, an intensive series of observations from the ground and from space, swung into action to pinpoint the source on the sky and track how its brightness changed. These observations in the gamma-ray, X-ray, optical, infrared, and radio showed that the optical/infrared counterpart was faint, evolved quickly, and became very red – the hallmarks of a kilonova.

“This type of explosion is very rapid, with the material in the explosion also expanding swiftly,” said Om Sharan Salafia, a co-author of the study at the INAF – Brera Astronomical Observatory in Italy. “As the whole cloud expands, the material cools off quickly and the peak of its light becomes visible in the infrared, and becomes redder on timescales of days to weeks.”

At later times it would have been impossible to study this kilonova from the ground, but these were the perfect conditions for Webb’s NIRCam (Near-Infrared Camera) and NIRSpec (Near-Infrared Spectrograph) instruments to observe this tumultuous environment. The spectrum has broad lines that show the material is ejected at high speeds, but one feature is clear: light emitted by tellurium, an element rarer than platinum on Earth.

The highly sensitive infrared capabilities of Webb helped scientists identify the home address of the two neutron stars that created the kilonova: a spiral galaxy about 120,000 light-years away from the site of the merger.

Prior to their venture, they were once two normal massive stars that formed a binary system in their home spiral galaxy. Since the duo was gravitationally bound, both stars were launched together on two separate occasions: when one among the pair exploded as a supernova and became a neutron star, and when the other star followed suit.

In this case, the neutron stars remained as a binary system despite two explosive jolts and were kicked out of their home galaxy. The pair travelled approximately the equivalent of the Milky Way galaxy’s diameter before merging several hundred million years later.

Scientists expect to find even more kilonovas in the future thanks to the increasing number of opportunities to have space and ground-based telescopes working in complementary ways to study changes in the Universe.

“Webb provides a phenomenal boost and may find even heavier elements,” said Ben Gompertz, a co-author of the study at the University of Birmingham in the United Kingdom. “As we get more frequent observations, the models will improve and the spectrum may evolve more in time. Webb has certainly opened the door to do a lot more, and its abilities will be completely transformative for our understanding of the Universe.”

These findings have been published in the journal Nature.

heavy element kilonova Bright galaxies and other light sources in various sizes and shapes are scattered across a black swath of space: small points, hazy elliptical-like smudges with halos, and spiral-shaped blobs. The objects vary in colour: white, blue-white, yellow-white, and orange-red. Toward the centre right is a blue-white spiral galaxy seen face-on that is larger than the other light sources in the image. — A team of scientists has used the NASA/ESA/CSA James Webb Space Telescope to observe an exceptionally bright gamma-ray burst, GRB 230307A, and its associated kilonova. Kilonovas—an explosion produced by a neutron star merging with either a black hole or with another neutron star—are extremely rare, making it difficult to observe these events. The highly sensitive infrared capabilities of Webb helped scientists identify the home address of the two neutron stars that created the kilonova.
This image from Webb’s NIRCam (Near-Infrared Camera) instrument highlights GRB 230307A’s kilonova and its former home galaxy among their local environment of other galaxies and foreground stars. The neutron stars were kicked out of their home galaxy and travelled the distance of about 120,000 light-years, approximately the diameter of the Milky Way galaxy, before finally merging several hundred million years later.
This image is a composite of separate exposures acquired by the James Webb Space Telescope using the NIRCam instrument. Several filters were used to sample wide wavelength ranges. The colour results from assigning different hues (colours) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colours are: Blue: F115W + F150W Green: F277W Red: F356W + F444W
Credit: NASA, ESA, CSA, STScI, A. Levan (IMAPP, Warw), A. Pagan (STScI)

Press release from ESA Webb

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Astronomy

Shadow playing with the red dwarf star TW Hydrae

By ScientifiCult 4 May 2023

Hubble follows shadow play around planet-forming disc: the young star TW Hydrae is playing ‘shadow puppets’ with scientists

In 2017 astronomers reported discovering a shadow sweeping across the face of a vast pancake-shaped disc of gas and dust surrounding the red dwarf star TW Hydrae. The shadow isn’t from a planet, but from an inner disc slightly inclined relative to the much larger outer disc — causing it to cast a shadow. One explanation is that an unseen planet’s gravity is pulling dust and gas into its inclined orbit. Now, a second shadow — playing a game of peek-a-boo — has emerged in just a few years between observations stored in the MAST archive of the NASA/ESA Hubble Space Telescope. This could be from yet another disc nestled inside the system. The two discs are likely evidence of a pair of planets under construction.

Hubble images TW Hydrae Disc Shadows (annotated). Comparison images from the NASA/ESA Hubble Space Telescope, taken several years apart, have uncovered two eerie shadows moving counterclockwise across a disc of gas and dust encircling the young star TW Hydrae. The discs are tilted face-on as seen from Earth and so give astronomers a bird’s-eye view of what’s happening around the star. The left image, taken in 2016, shows just one shadow [A] at the 11 o’clock position. This shadow is cast by an inner disc that is slightly inclined to the outer disc and so blocks starlight. The picture on the left shows a second shadow that emerged from yet another nested disc at the 7 o’clock position, as photographed in 2021. What was originally the inner disc is marked [B] in this later view. The shadows rotate around the star at different rates like the hand on a clock. They are evidence for two unseen planets that have pulled dust into their orbits. This makes them slightly inclined to each other. This is a visible-light photo taken with the Space Telescope Imaging Spectrograph. Artificial colour has been added to enhance details.
Credit: NASA, ESA, J. Debes STScI

TW Hydrae is less than 10 million years old and resides about 200 light-years away. In its infancy, some 4.6 billion years ago, our Solar System may have resembled the TW Hydrae system. Because the TW Hydrae system is tilted nearly face-on as seen from Earth, it is an optimum target for getting a bird’s-eye view of a planetary construction yard.

The second shadow was discovered in observations obtained on 6 June 2021, as part of a multi-year programme designed to track the shadows in circumstellar discs. John Debes of AURA/STScI for the European Space Agency at the Space Telescope Science Institute in Baltimore, Maryland, compared these latest observations of the TW Hydrae disc to Hubble observations made several years ago.

“We found out that the shadow had done something completely different,” said Debes, who is principal investigator and lead author of the study published in The Astrophysical Journal. “When I first looked at the data, I thought something had gone wrong with the observation because it wasn’t what I was expecting. I was flummoxed at first, and all my collaborators were like: what is going on? We really had to scratch our heads and it took us a while to actually figure out an explanation.”

“We hatched a theory of what might be causing the changing shadows,” added Rebecca Nealon, a member of the science team at the University of Warwick in the United Kingdom. “But to test this we had to run sophisticated models where we varied the number of discs and their orientations to try to reproduce Hubble’s observations.”

shadow TW Hydrae — Concentric gas and dust discs around the star TW Hydrae. This illustration is based on NASA/ESA Hubble Space Telescope images of a gas and dust discs encircling the young star TW Hydrae. Hubble photos show shadows sweeping across the discs encircling the system. The interpretation is that these shadows are from slightly inclined inner discs that block starlight from reaching the outer disc, and therefore cast a shadow. The discs are slightly inclined to each other because of the gravitational pull of unseen planets warping the disc structure. Credit: NASA. ESA, L. Hustak (STScI)

The best solution the team came up with is that there are two misaligned discs casting shadows. They were so close to each other in the earlier observation they were missed. Over time they’ve now separated and split into two shadows.

“We’ve never really seen this before on a protoplanetary disc. It makes the system much more complex than we originally thought,” said Debes.

The simplest explanation is that the misaligned discs are likely caused by the gravitational pull of two planets in slightly different orbital planes. Hubble is piecing together a holistic view of the architecture of the system.

The discs may be proxies for planets that are lapping each other as they whirl around the star. It’s sort of like spinning two vinyl records at slightly different speeds. Sometimes the labels will match up but then one gets ahead of the other.

“It does suggest that the two planets have to be fairly close to each other. If one was moving much faster than the other, this would have been noticed in earlier observations. It’s like two racing cars that are close to each other, but one slowly overtakes and laps the other,” said Debes.

The suspected planets are located in a region roughly the distance of Jupiter from our Sun. And the shadows complete one rotation around the star about every 15 years — the orbital period that would be expected at that distance from the star.

Also, these two inner discs are inclined by about five to seven degrees relative to the plane of the outer disc. This is comparable to the range of orbital inclinations inside our Solar System.

“This is right in line with typical Solar System-style architecture,” said Debes.

The outer disc that the shadows are falling on may extend as far as several times the radius of our Solar System’s Kuiper belt. This larger disc has a curious gap at twice Pluto’s average distance from the Sun. This might be evidence for a third planet in the system.

Any inner planets would be difficult to detect because their light would be lost in the glare of the star. Also, dust in the system would dim their reflected light. ESA’s Gaia space observatory may be able to measure a wobble in the star if Jupiter-mass planets are tugging on it, but this would take years given the long orbital periods.

The TW Hydrae data are from Hubble’s Space Telescope Imaging Spectrograph. The NASA/ESA/CSA James Webb Space Telescope’s infrared vision may also be able to show the shadows in more detail.

Hubble images TW Hydrae Disc Shadows (clean). Comparison images from the NASA/ESA Hubble Space Telescope, taken several years apart, have uncovered two eerie shadows moving counterclockwise across a disc of gas and dust disc encircling the young star TW Hydrae. The discs are tilted face-on as seen from Earth and so give astronomers a bird’s-eye view of what’s happening around the star. The left image, taken in 2016, shows just one shadow at the 11 o’clock position. This shadow is cast by an inner disc that is slightly inclined to the outer disc and so blocks starlight. The picture on the left shows a second shadow that emerged from yet another nested disc at the 7 o’clock position, as photographed in 2021. The shadows rotate around the star at different rates like the hands of a clock. They are evidence for two unseen planets that have pulled dust into their orbits. This makes them slightly inclined to each other. This is a-visible light photo taken with the Space Telescope Imaging Spectrograph. Artificial colour has been added to enhance details. Credit: NASA, ESA, J. Debes STScI

Press release from ESA Hubble.

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