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Starts With A Bang

Did JWST plus ALMA just reveal how pulsars form?

In 1987, the closest supernova directly observed in nearly 400 years occurred. Will a pulsar arise from those ashes? JWST offers clues.
SN 1987a JWST
The central region of supernova remnant SN 1987A, as seen for the first time by JWST's NIRCam instrument in 2023. The gaseous and dusty features in the interior of the remnant have been revealed in greater detail by JWST than any observatory previous, as core-collapse supernovae are incredible sites for the production of cosmic dust.
Credit: NASA, ESA, CSA, Mikako Matsuura (Cardiff University), Richard Arendt (NASA-GSFC, UMBC), Claes Fransson (Stockholm University), Josefin Larsson (KTH); Processing: Alyssa Pagan (STScI)
Key Takeaways
  • In 1987, humanity observed a supernova in the galaxy just next door: in the Large Magellanic Cloud only ~165,000 light-years away, known as SN 1987A.
  • Although other core-collapse supernovae have led to the creation of pulsars, such as within the Crab Nebula, no pulsing remnant has ever been associated with SN 1987A.
  • But with recent observations by both ALMA and JWST, we’ve now seen unprecedented details within the supernova remnant, suggesting a path for this object to eventually become a pulsar.

In 1987, humanity observed the closest supernova since 1604.

nasa kepler's supernova remnant spitzer
In 1604, the last naked-eye supernova to occur in the Milky Way galaxy happened, known today as Kepler’s supernova. Although the supernova faded from naked-eye view by 1605, its remnant remains visible today, as shown here in an X-ray/optical/infrared composite. The bright yellow “streaks” are the only component still visible in the optical, more than 400 years later.
Credit: NASA, R. Sankrit (NASA Ames) and W.P. Blair (Johns Hopkins Univ.)

From 165,000 light-years away, a blue supergiant star’s core collapsed.

SN 1987a supernova remnant
This optical image, taken with the Hubble Space Telescope in 2017, shows supernova remnant SN 1987A precisely 30 years after its detonation was observed. Located ~165,000 light-years away in the Large Magellanic Cloud, on the outskirts of the Tarantula Nebula, this is the first and only supernova caught within our Local Group in the last 100+ years.
Credit: NASA, ESA, and R. Kirshner (Harvard-Smithsonian Center for Astrophysics and Gordon and Betty Moore Foundation) and P. Challis (Harvard-Smithsonian Center for Astrophysics)

The first observed signals were neutrinos: arriving in a ~12-second burst.

SN 1987a neutrinos
Three different detectors observed the neutrinos from SN 1987A, with KamiokaNDE the most robust and successful. The transformation from a nucleon decay experiment to a neutrino detector experiment would pave the way for the developing science of neutrino astronomy. The light from the supernova would not arrive until hours later.
Credit: Riya and Astroriya/Wikimedia Commons

Hours later, the light arrived, indicating a core-collapse supernova.

Subsequently, we’ve meticulously observed the expanding, evolving remnant.

This image shows the supernova remnant of SN 1987A in six different wavelengths of light. Even though it’s been 36 years since this explosion occurred, and even though it’s right here in our own backyard, the material around the central engine has not cleared enough to expose the stellar remnant. For contrast, Cow-like objects (also known as fast blue optical transients) have their cores exposed almost immediately.
Credit: Alak Ray, Nature Astronomy, 2017; ACTA/ALMA/ESO/Hubble/Chandra composite

On the outskirts, gaseous shells blown off centuries earlier continue expanding.

sn 1987a remnant
The remnant of SN 1987A, located in the Large Magellanic Cloud some 165,000 light years away. It was the closest observed supernova to Earth in more than three centuries, and reached a maximum magnitude of +2.8, clearly visible to the naked eye and significantly brighter than the host galaxy containing it.
Credit: ESA/Hubble & NASA

Interior to them, supernova shockwaves heat a spheroidal halo of material.

SN 1987a hubble chandra radio
Hubble’s optical light observations of SN 1987A become even more valuable when they are combined with observations from telescopes that can measure other kinds of radiation from the exploding star. The image shows the evolving images of hot spots from the Hubble Telescope alongside images taken at approximately the same time from the Chandra X-ray Observatory and the Australia Telescope Compact Array (ATCA) radio observatory. The X-ray images show an expanding ring of gas, hotter than a million degrees, that has evidently reached the optical ring at the same time as the hot spots appeared. The radio images show a similar expanding ring of radio emission, caused by electrons moving through magnetized matter at nearly the speed of light.
Credit: R. McCray (University of Colorado), D. Burrows and S. Park (Pennsylvania State University), and R. Manchester (Australia Telescope National Facility)

Energy injection causes irregular changes in brightness, X-rays, and radio emissions.

A diagram displaying a ring of stars and the JWST.
Compact array observations at long wavelengths show that the remnant continues to expand, and the interstellar luminosity continues to rise surrounding the initial explosion. The brightness in a variety of wavelengths of light continues to evolve as different forms of ejecta slam into the surrounding material and heat it up, causing it to radiate.
Credit: Lister Staveley-Smith (UWA), Lewis Ball (ATNF), Bryan Gaensler (USyd), Mike Kesteven (ATNF), Dick Manchester (ATNF) and Tasso Tzioumis (ATNF)

But the inner region of this explosion remains mysterious.

SN 1987a Chandra x-ray
The outward-moving shockwave of material from the 1987 explosion continues to collide with previous ejecta from the formerly massive star, heating and illuminating the material when collisions occur. A wide variety of observatories continue to image the supernova remnant today, tracking its evolution. However, the innermost region remains heavily dust-obscured, preventing us from truly knowing what’s going on inside.
Credit: J. Larsson et al., ApJ, 2019

The collapsing core should create a massive remnant: a neutron star.

crab pulsar nebula multiwavelength
Five different combined wavelengths show the true magnificence and diversity of phenomena at play in the Crab Nebula. The X-ray data, in purple, shows the hot gas/plasma created by the central pulsar, which is clearly identifiable in both the individual and the composite image. This nebula arose from a massive star that died in a core-collapse supernova back in 1054, where a bright light appeared worldwide, allowing us, at present, to reconstruct this historical event.
Credit: G. Dubner (IAFE, CONICET-University of Buenos Aires) et al.; NRAO/AUI/NSF; A. Loll et al.; T. Temim et al.; F. Seward et al.; Chandra/CXC; Spitzer/JPL-Caltech; XMM-Newton/ESA; and Hubble/STScI

1054’s similar supernova gave rise to today’s Crab pulsar.

crab pulsar remnant
A combination of X-ray, optical, and infrared data reveal the central pulsar at the core of the Crab Nebula, including the winds and outflows that the pulsars carry in the surrounding matter. The central bright purplish-white spot is, indeed, the Crab pulsar, which itself spins at about 30 times per second. The material shown here spans about 5 light-years in extent, originating from a star that went supernova about 1,000 years ago, teaching us that the typical speed of the ejecta is around 1,500 km/s. The neutron star originally reached a temperature of ~1 trillion K, but even now, it’s already cooled to “only” about 600,000 K.
Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech

Nevertheless, no pulsing neutron star is associated with SN 1987A.

hypermassive neutron star
This image shows the illustration of a massive neutron star, along with the distorted gravitational effects an observer might see if they had the capability of viewing this neutron star at such a close distance. While neutron stars are famous for pulsing, not every neutron star is a pulsar. The fastest pulsars, known as millisecond pulsars, rotate at more than 100 times per second, with the current record holder completing a whopping 766 rotations each second.
Credit: Daniel Molybdenum/flickr and raphael.concorde/Wikimedia Commons

However, two clues suggest that one may be developing.

ALMA multiwavelength SN 1987a remnant
As the core region of the SN 1987A remnant continues to evolve, the central dusty region will cool off and much of the radiation obscured from it will become visible, while the central remnant will continue to cool and evolve as well. It’s conceivable, when this occurs, that periodic radio pulses will become observable, revealing whether the central neutron star is a pulsar or not.
Credit: ALMA (ESO/NAOJ/NRAO), P. Cigan and R. Indebetouw; NRAO/AUI/NSF, B. Saxton; NASA/ESA

ALMA observations reveal enormous quantities of interior gas and dust.

Nasa's supermassive black hole observed using the JWST.
Extremely high-resolution ALMA images revealed a hot “blob” in the dusty core of SN 1987A (inset), which could be the location of the expected neutron star. The red color shows dust and cold gas in the center of the supernova remnant, taken at radio wavelengths with ALMA. The green and blue hues reveal where the expanding shock wave from the exploded star is colliding with a ring of material around the supernova. An observatory like JWST is perfect for revealing the matter in the “dark” regions of this image.
Credit: ALMA (ESO/NAOJ/NRAO), P. Cigan and R. Indebetouw; NRAO/AUI/NSF, B. Saxton; NASA/ESA

A central “hot spot” suggests a newborn neutron star’s presence.

alma central core gas SN 1987a
In the center of the remnant of SN 1987A, ALMA, with its incredible resolution and long-wavelength capabilities, was able to observe a particularly hot spot within the gas and dust of SN 1987A. The extra heat is thought by many to be an indicator of a young neutron star, which would make this the youngest neutron star ever discovered.
Credit: P. Cigan et al./Cardiff University

Now, JWST has chimed in, showcasing its unique views.

annotated SN 1987a JWST Webb features
Webb’s NIRCam (Near-Infrared Camera) captured this detailed image of SN 1987A, which has been annotated to highlight key structures. At the center, material ejected from the supernova forms a keyhole shape. Just to its left and right are faint crescents newly discovered by Webb. Beyond them an equatorial ring, formed from material ejected tens of thousands of years before the supernova explosion, contains bright hot spots. Exterior to that is diffuse emission and two faint outer rings.
Credit: NASA, ESA, CSA, Mikako Matsuura (Cardiff University), Richard Arendt (NASA-GSFC, UMBC), Claes Fransson (Stockholm University), Josefin Larsson (KTH); Processing: Alyssa Pagan (STScI)

Newly revealed features include “crescents” appearing in the gas.

SN 1987a JWST
The innermost region of the remnant of SN 1987A, as revealed by JWST, shows gas, light-blocking dust at the center, and crescent-like shapes all interior to the spheroidal region of hot gas being impacted by the supernova ejecta. The crescent features, in particular, have never been seen by any telescope prior to JWST, and its nature has yet to be uncovered.
Credit: NASA, ESA, CSA, Mikako Matsuura (Cardiff University), Richard Arendt (NASA-GSFC, UMBC), Claes Fransson (Stockholm University), Josefin Larsson (KTH); Processing: Alyssa Pagan (STScI)

Are they mundane ejecta, or shapes carved by magnetic fields?

Sn 1987a remnant
A supernova explosion enriches the surrounding interstellar medium with heavy elements. This illustration, of the remnant of SN 1987A, showcases how the material from a dead star gets recycled into the interstellar medium. However, precisely what’s occurring at the center of the remnant is obscure, as even JWST’s powerful NIRCam imager cannot fully penetrate the light-blocking dust to see inside.
Credit: ESO/L. Calçada

The supernova remnant’s evolution will ultimately reveal whatever object is inside.

hand of god pulsar wind nebula
A small, dense object only twelve miles in diameter is responsible for this X-ray nebula that spans ~150 light-years. This pulsar is spinning around almost 7 times a second and has a magnetic field at its surface estimated to be 15 trillion times stronger than the Earth’s magnetic field. This pulsar wind nebula exhibits spectacular details that can only be revealed, at present, with the power of NASA’s Chandra X-ray observatory.
Credit: NASA/CXC/CfA/P. Slane et al.

It’s possible we are witnessing the formation of our Local Group’s newest pulsar.

neutron star magnetic field
This computer simulation of a neutron star shows charged particles being whipped around by a neutron star’s extraordinarily strong electric and magnetic fields. It is possible that a neutron star has formed within the remnant of SN 1987A, but the region is still too dusty and gas-rich for the “pulses” to seep out.
Credit: NASA’s Goddard Space Flight Center

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