A New Type of Stellar Explosion: The ‘Kilonova’

If you were to compare the universe to a food item, envisioning it as a bag of microwave popcorn is quite fitting, filled with intense heat and explosive chaos on all sides. Novae, supernovae, hypernovae—such stellar explosions happen frequently in the universe. However, when astronomers discover a completely different kind of explosion, it can be considered a rare event.

A nova is a stellar explosion caused by the disruption of a white dwarf star, whereas supernova explosions occur in stars with masses greater than 1.4 times that of the sun. This June, NASA’s Hubble Space Telescope detected a new kind of stellar explosion called a kilonova. This type of explosion is observed when two highly dense objects, such as neutron stars, collide. Hubble observed a dimming fireball from a kilonova. Shortly after, Hubble detected a minor gamma-ray burst four billion light-years away from Earth. According to Professor Nial Tanvir of the University of Leicester, who led the research team, this observation has finally unveiled the mystery surrounding short gamma-ray bursts.

A gamma-ray burst is a flare or spark produced by high-energy radiation. Such sparks can be seen scattered throughout space during gamma-ray bursts. These come in two varieties: some are short, and some long. It is believed that long-duration gamma-ray bursts (lasting more than two seconds) are produced when extremely massive stars collapse. Tanvir’s team and many other astronomers believe this, and substantial evidence has already been presented for this theory. Although scientists have a clear understanding of long gamma-ray bursts, the short ones remain quite mysterious.

While it was theorized that short gamma-ray bursts are triggered by the merging of dense objects like neutron stars, scientists previously lacked solid evidence for this. Thanks to Hubble’s observations, researchers have now been able to present definitive proof.

Astrophysicists had already suspected that a pair of highly dense neutron stars in a binary system could create a short gamma-ray burst as they spiral towards each other. This occurs because the system emits gravitational radiation, causing small ripples in the fabric of spacetime. The energy loss due to these minor waves causes the two objects to rapidly draw closer. Just milliseconds before the explosion, the two stars spiral into one another and come into contact. As a result, highly radioactive matter is ejected all around. This radioactive matter heats up and expands, releasing streams of visible light.

A kilonova produced in this way ranks mid-range in terms of brightness among stellar explosions. It is a thousand times brighter than a nova but only produces one-tenth or even one-hundredth the brightness of a supernova. Daniel Kasen, an astrophysicist from the University of California, developed a new calculation that has greatly helped scientists understand what a kilonova might look like, even though he was not involved in the research. Kasen was working on creating a theoretical model of kilonovae. He predicted that the hot plasma responsible for radiation would block visible light and that, through the massive energy release of the kilonova, infrared light would dominate for several days. He advised scientists: “To detect these, you should focus on the infrared spectrum, even though this has never been done before.”

Nial Tanvir used the Hubble Telescope to search for gamma-ray bursts in the infrared spectrum and to observe the debris emerging from neutron star explosions. Despite lasting only a tenth of a second, NASA’s high-speed telescope managed to capture it on June 3rd, categorizing it as GRB1306030B. An independent analysis of data from another research team confirmed the discovery. Kasen described this observation as excellent, noting how challenging it was since the explosion was distant and fleeting. Nevertheless, it proved that the merging of two objects produced the observed infrared glow—this is the kilonova. The research findings were published online in a special August 3rd edition of the journal Nature.

In a vast place like the universe, discovering a new kind of cosmic phenomenon is both extremely difficult and quite natural. Much has been discovered, yet presumably a great deal remains unknown. The universe is a place full of surprises and endless opportunities to expand our knowledge. The discovery of the kilonova is just a small example. The universe, with its infinite dark vastness, awaits us with its store of mysteries and beckons us: “Come, teams of the curious, come, teams of the intelligent. Uncover all my secrets; solve every puzzle with your intellect, wisdom, and hard work.” Who knows which mysteries of the universe will be unlocked next? What further wonders might await us—who can say?

Sources:
The Kilonova: A New Kind Of Cosmic Blast – www.popularmechaniscs.com
HUBBLE SEES THE FIREBALL FROM A ‘‘KILONOVA’’ – NASA .