Did JWST plus ALMA just reveal how pulsars form?

In 1987, humanity observed the closest supernova since 1604.

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.

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

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.

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

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.

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.

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

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.

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

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.

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

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.

But the inner region of this explosion remains mysterious.

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.

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

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.

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

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.

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

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.

However, two clues suggest that one may be developing.

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.

ALMA observations reveal enormous quantities of interior gas and dust.

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.