Astronomers think a long GRB (gamma-ray burst) arises from a massive, rapidly rotating star when its core runs out of fuel and collapses, forming a black hole in the star's center. In this artist's concept, two jets emerge from the dying star and interact with surrounding gas and dust.
'Everyone in that group was like, 'this thing's crazy! Who's on duty to analyze this? This is what we've been waiting for,'' Lesage, a graduate student at the
The unusual event turned to be a cosmic burst that may have been the brightest at X-ray and gamma-ray energies since civilization began. Astronomers dubbed it the BOAT, 'the brightest of all time.' Lesage led an analysis of Fermi data that demonstrated just how bright the BOAT really was. More than 150 telescopes in space and on Earth followed up to get more details of the event including
The Universe is Changing
The BOAT is an example of what astronomers call Time-Domain and Multimessenger Astronomy. The 'Time Domain' part refers to events that happen in the universe that telescopes can observe as they unfold, such as a supernova or the merger of two neutron stars. 'Multimessenger Astronomy' refers to the variety of 'messengers' that deliver information from the universe, including all forms of light, high-energy particles, and ripples in spacetime called gravitational waves.
While the universe may seem like it changes extremely slowly, over millions or even billions of years, its celestial occupants do sometimes produce dramatic changes on the order of days or even fractions of seconds. Galactic centers brighten as their central black holes eat material. Black holes siphon plasma from nearby stars. Stars explode. Neutron stars collide with black holes, neutron stars collide with neutron stars, and black holes merge with black holes. Even distant crashes of celestial objects can send powerful ripples that can be detected by space- and ground-based telescopes and instruments. Many of these phenomena are unpredictable in terms of both where and when they might happen next.
NASA has two 'watchdog' satellites with wide fields of view that send out alerts when they detect a sudden brightening of gamma rays: Fermi and Swift. Fermi's Gamma-Ray Burst Monitor and Large Area Telescope, and Swift's Burst Alert Telescope, are key instruments that might be the first to observe these events.
'When something impulsive happens, when something goes boom and explodes or something goes crunch and collapses, they trigger,' said
Once scientists receive an alert on their computers and phones, they may be able to collaborate with other telescopes to follow up on the event. By using a variety of different space-based observatories and instruments to study these largely unpredictable flashes, scientists can piece together what, where, when, and why they observed a 'blip' in the usual calm of space.
After comparing observations of the BOAT from numerous telescopes, scientists determined that this unusually bright burst came from a supernova and specifically, the core collapse of a massive star rotating rapidly. Later, with data from
'A giant star just exploded, and we get to study it and figure out what happened, and reverse engineer the pieces and put it back together,' Lesage said.
Time-domain astronomy lets us get fundamental answers on the properties of the universe, of fundamental physics itself, and the origin of the elements.'
Astrophysicist,
New Bright Signals
Just five months after the BOAT, scientists received an alert from Fermi about the second-brightest gamma-ray burst seen in the last 50 years. This newer signal, GRB 230307A, which happened in
This result still puzzles astronomers such as
'Time-domain astronomy lets us get fundamental answers on the properties of the universe, of fundamental physics itself, and the origin of the elements,' Burns said.
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 color: white, blue-white, yellow-white, and orange-red. Toward the center right is a blue-white spiral galaxy seen face-on that is larger than the other light sources in the image. The galaxy is labeled 'former home galaxy.' Toward the upper left is a small red point, which has a white circle around it and is labeled 'GRB 230307A kilonova.'
This image from
A Multitude of Messengers
Cosmic 'messengers' associated with fleeting cosmic blips also help scientists reconstruct their origins. The initial 2015 discovery of gravitational waves by LIGO, the
In 2017, scientists demonstrated that potential by combining gravitational wave observations with data from many different ground and space-based observatories to study a kilonova, or neutron star merger, called GW170817. Among the insights from the extensive study of this kilonova, Burns and colleagues used it to make the first precise measurement of the speed of gravity, 'the last major confirmation of a prediction from Einstein,' he said.
Today, the network of the
This animation shows what happened in the nine days after a neutron star merger detected in 2017. First, a pair of glowing blue neutron stars spiral quickly toward each other, merging with a bright flash. The merger creates gravitational waves (shown as pale arcs rippling outward), a near-light-speed jet that produced gamma rays (shown as brown cones and a rapidly traveling magenta glow erupting from the center of the collision), and a donut-shaped ring of expanding blue debris around the center of the explosion. A variety of colors represent the wavelengths of light produced by the kilonova, creating violet to blue-white to red bursts above and below the collision.
Doomed neutron stars whirl toward their demise in this illustration. Gravitational waves bleed away orbital energy, causing the stars to move closer together and merge. As they collide, some of the debris blasts away in particle jets moving at nearly the speed of light, producing a brief burst of gamma rays.
Light is the only kind of 'messenger' from the universe that has been detected for both the BOAT and the gamma-ray burst that seems to have produced tellurium. An experiment near the
'This multimessenger approach is important, even when you don't have a detection,' said
A
For Lesage, who is writing his dissertation about the BOAT, time-domain and multimessenger astronomy is an exciting area of study. The BOAT itself is still keeping him and other astronomers busy as they look at all of the processes revealed by the exceptionally bright light from this extreme event. But more transient events are sure to come, and will keep scientists on their toes as they chase after them with a wide variety of telescopes and instruments.
'That's just transient events-look now or you're going to miss it,' Lesage said. 'Look as quickly as you possibly can.'
When this animation opens, there are concentric rings of pale blue the expand away and off the screen. At the center is a bright ball of light with two narrow cones of orange, fiery-looking material extend in opposing directions, tilted just to the right. During the first few seconds, there are magenta flashes of light that seem to be pushed along with the ends of the orange cones. The central ball expands into a puffy, electric blue cloud. The sequence represents the events that happened after two neutron stars merged, exploding in a gamma-ray burst.
This animation captures phenomena observed over the course of nine days following the neutron star merger known as GW170817, detected on
Further Reading: Telescopes on the Case
In the next few years NASA will be launching new 'watcher' satellites to help look out for sudden transient events like these. They include several CubeSats, which are a class of miniaturized spacecraft built in standardized units of cubes around 4 inches (10 cm) on a side:
BurstCube, launching in
ULTRASAT (Ultraviolet Transient Astronomy Satellite), a small satellite from the
Additionally, NASA telescopes with other primary goals can help look out for these unusual events:
Psyche, on its way to the metal-rich asteroid Psyche, has a gamma-ray spectrometer that astronomers can use to detect gamma-ray bursts as the spacecraft cruises toward its destination over the next several years.
WISE, which mapped the sky at infrared wavelengths, found many new distant objects and cosmic phenomena. The NEOWISE mission, which reuses the WISE telescope, surveys near-Earth space for potentially hazardous asteroids.
The NEO Surveyor mission will use infrared detectors to broaden the search for asteroids and comets that may pose a hazard to the Earth. The images to be taken by NEO Surveyor also are expected to capture many more distant background objects.
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