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4 months ago

5 Unpredictable Things Swift Has Studied (and 1 It’s Still Looking For)

Our Neil Gehrels Swift Observatory — Swift for short — is celebrating its 20th anniversary! The satellite studies cosmic objects and events using visible, ultraviolet, X-ray, and gamma-ray light. Swift plays a key role in our efforts to observe our ever-changing universe. Here are a few cosmic surprises Swift has caught over the years — plus one scientists hope to see.

This sequence shows X-rays from the initial flash of GRB 221009A that could be detected for weeks as dust in our galaxy scattered the light back to us. This resulted in the appearance of an extraordinary set of expanding rings, here colored magenta, with a bright yellow spot at the center. The images were captured over 12 days by the X-ray Telescope aboard NASA’s Neil Gehrels Swift Observatory. Credit: NASA/Swift/A. Beardmore (University of Leicester)

#BOAT

Swift was designed to detect and study gamma-ray bursts, the most powerful explosions in the universe. These bursts occur all over the sky without warning, with about one a day detected on average. They also usually last less than a minute – sometimes less than a few seconds – so you need a telescope like Swift that can quickly spot and precisely locate these new events.

In the fall of 2022, for example, Swift helped study a gamma-ray burst nicknamed the BOAT, or brightest of all time. The image above depicts X-rays Swift detected for 12 days after the initial flash. Dust in our galaxy scattered the X-ray light back to us, creating an extraordinary set of expanding rings.

This gif illustrates what happens when an unlucky star strays too close to a monster black hole. Gravitational forces create intense tides that break the star apart into a stream of gas. The trailing part of the stream escapes the system, while the leading part swings back around, surrounding the black hole with a disk of debris. This cataclysmic phenomenon is called a tidal disruption event. This image is watermarked “Artist’s concept.” Credit: NASA’s Goddard Space Flight Center/Chris Smith (USRA/GESTAR)

Star meets black hole

Tidal disruptions happen when an unlucky star strays too close to a black hole. Gravitational forces break the star apart into a stream of gas, as seen above. Some of the gas escapes, but some swings back around the black hole and creates a disk of debris that orbits around it.

These events are rare. They only occur once every 10,000 to 100,000 years in a galaxy the size of our Milky Way. Astronomers can’t predict when or where they’ll pop up, but Swift’s quick reflexes have helped it observe several tidal disruption events in other galaxies over its 20-year career.

This gif illustrates various features of a galaxy's outburst. The black hole in the center is surrounded by a puffy orange disk of gas and dust. Above and below the center of the disk are blue cones representing the corona. At the start of the sequence, a flash of purple-white light travels from the edges of the disk inward, until the whole thing is illuminated. That light fades and then there is a flare of blue light above and below the center. This image is watermarked “Artist’s concept.” Credit: NASA’s Goddard Space Flight Center

Active galaxies

Usually, we think of galaxies – and most other things in the universe – as changing so slowly that we can’t see the changes. But about 10% of the universe’s galaxies are active, which means their black hole-powered centers are very bright and have a lot going on. They can produce high-speed particle jets or flares of light. Sometimes scientists can catch and watch these real-time changes.

For example, for several years starting in 2018, Swift and other telescopes observed changes in a galaxy’s X-ray and ultraviolet light that led them to think the galaxy’s magnetic field had flipped 180 degrees.

This animation depicts a giant flare on the surface of a magnetar. The object’s glowing surface, covered in swirls of lighter and darker blue, fills the lower right corner of the image. The powerful magnetic field surrounding this stellar corpse is represented by thin white speckled loops that arc off the surface and continue past the edges of the image. A starquake rocks the surface of the magnetar, abruptly affecting its magnetic field and producing a quick, powerful pulse of X-rays and gamma rays, represented by a magenta glow. The event also ejects electrons and positrons traveling at about 99% the speed of light. These are represented by a blue blob, which follows the gamma rays heading towards the upper left and off-screen. The image is watermarked “Artist’s concept.” Credit: NASA’s Goddard Space Flight Center/Chris Smith (USRA/GESTAR)

Magnetic star remnants

Magnetars are a type of neutron star, a very dense leftover of a massive star that exploded in a supernova. Magnetars have the strongest magnetic fields we know of — up to 10 trillion times more intense than a refrigerator magnet and a thousand times stronger than a typical neutron star’s.

Occasionally, magnetars experience outbursts related to sudden changes in their magnetic fields that can last for months or even years. Swift detected such an outburst from a magnetar in 2020. The satellite’s X-ray observations helped scientists determine that the city-sized object was rotating once every 10.4 seconds.

This gif shows six snapshots of comet 2I/Borisov as it traveled through our solar system. They were captured with the Ultraviolet/Optical Telescope aboard NASA’s Neil Gehrels Swift Observatory. The first four images are a dark purple color with streaks of white traveling across them. Borisov is a faint white smudge in the center. The fifth image has a blue background with the same white streaks. The last image is just the blue background. The image is watermarked with “Ultraviolet” on the left side. On the right are rotating labels showing the date of each snapshot: Sept 27, Nov 1, Dec 1, Dec 21, Jan 14, Feb 17. Credit: NASA/Swift/Z. Xing et al. 2020

Comets

Swift has also studied comets in our own solar system. Comets are town-sized snowballs of frozen gases, rock, and dust. When one gets close to our Sun, it heats up and spews dust and gases into a giant glowing halo.

In 2019, Swift watched a comet called 2I/Borisov. Using ultraviolet light, scientists calculated that Borisov lost enough water to fill 92 Olympic-size swimming pools! (Another interesting fact about Borisov: Astronomers think it came from outside our solar system.)

This animation shows a spacecraft, NASA’s Neil Gehrels Swift Observatory, in orbit above Earth. Swift is composed of a long cylinder at the center, wrapped in golden foil. At the front of the cylinder is a silver sunshade protruding over several telescopes. Two black solar arrays are attached on either side of the cylinder, extending like wings. The animation begins with a view of Swift with Earth in the background. Then the camera pans along one side of the spacecraft until Swift is seen looking out into space. Credit: NASA's Goddard Space Flight Center Conceptual Image Lab

What's next for Swift?

Swift has studied a lot of cool events and objects over its two decades, but there are still a few events scientists are hoping it’ll see.

Swift is an important part of a new era of astrophysics called multimessenger astronomy, which is where scientists use light, particles, and space-time ripples called gravitational waves to study different aspects of cosmic events.

A cartoon of different cosmic messengers. On top are particles, which show as four different colored dots that have trails appearing behind them, evoking movement. In the middle is light, which is shown as a wave moving through space. On the bottom are gravitational waves. These are shown as a series of ovals that expand and contract in sequence to evoke the feeling of an elastic tube that is growing and shrinking in width. The image is watermarked “Artist’s concept.” Credit: NASA’s Goddard Space Flight Center

In 2017, Swift and other observatories detected light and gravitational waves from the same event, a gamma-ray burst, for the first time. But what astronomers really want is to detect all three messengers from the same event.

As Swift enters its 20th year, it’ll keep watching the ever-changing sky.

Keep up with Swift through NASA Universe on X, Facebook, and Instagram. And make sure to follow us on Tumblr for your regular dose of space!

What is a Magnetar?

A magnetar is a type of neutron star with an extremely powerful magnetic field, the decay of which powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays.1

History

On March 5, 1979, several months after dropping probes into the toxic atmosphere of Venus, two Soviet spacecraft, Venera 11 and 12, were drifting through the inner solar system on an elliptical orbit. It had been an uneventful cruise. The radiation readings on board both probes hovered around a nominal 100 counts per second. But at 10:51AM EST, a pulse of gamma radiation hit them. Within a fraction of a millisecond, the radiation level shot above 200,000 counts per second and quickly went off scale.

Eleven seconds later gamma rays swamped the NASA space probe Helios 2, also orbiting the sun. A plane wave front of high-energy radiation was evidently sweeping through the solar system. It soon reached Venus and saturated the Pioneer Venus Orbiter’s detector. Within seconds the gamma rays reached Earth. They flooded detectors on three U.S. Department of Defense Vela satellites, the Soviet Prognoz 7 satellite, and the Einstein Observatory. Finally, on its way out of the solar system, the wave also blitzed the International Sun-Earth Explorer.

The pulse of highly energetic, or “hard,” gamma rays was 100 times as intense as any previous burst of gamma rays detected from beyond the solar system, and it lasted just two tenths of a second. At the time, nobody noticed; life continued calmly beneath our planet’s protective atmosphere. Fortunately, all 10 spacecraft survived the trauma without permanent damage. The hard pulse was followed by a fainter glow of lower-energy, or “soft,” gamma rays, as well as x-rays, which steadily faded over the subsequent three minutes. As it faded away, the signal oscillated gently, with a period of eight seconds. Fourteen and a half hours later, at 1:17AM on March 6, another, fainter burst of x-rays came from the same spot on the sky. Over the ensuing four years, Evgeny P. Mazets of the Ioffe Institute in St. Petersburg, Russia, and his collaborators detected 16 bursts coming from the same direction. They varied in intensity, but all were fainter and shorter than the March 5 burst.

Astronomers had never seen anything like this. For want of a better idea, they initially listed these bursts in catalogues alongside the better-known gamma-ray bursts (GRBs), even though they clearly differed in several ways. In the mid-1980s Kevin C. Hurley of the University of California at Berkeley realized that similar outbursts were coming from two other areas of the sky. Evidently these sources were all repeating unlike GRBs, which are one-shot events [see “The Brightest Explosions in the Universe,” by Neil Gehrels, Luigi Piro and Peter J. T. Leonard; Scientific American, December 2002]. At a July 1986 meeting in Toulouse, France, astronomers agreed on the approximate locations of the three sources and dubbed them “soft gamma repeaters” (SGRs). The alphabet soup of astronomy had gained a new ingredient.

Another seven years passed before two of us (Duncan and Thompson) devised an explanation for these strange objects, and only in 1998 did one of us (Kouveliotou) and her team find remains of a star that exploded 5,000 years ago. Unless this overlap was pure coincidence, it put the source 1,000 times as far away as theorists had thought—and thus made it a million times brighter than the Eddington limit. In 0.2 second the March 1979 event released as much energy as the sun radiates in roughly 10,000 years, and it concentrated that energy in gamma rays rather than spreading it across the electromagnetic spectrum.2

About 26 magnetars are known (see here).

1 http://en.wikipedia.org/wiki/Magnetar

2 http://solomon.as.utexas.edu/~duncan/sciam.pdf