Seventeen years ago, astronomers observed that a 40 million light-years distant supernova explodes in the galaxy called NGC 7424 in the southern constellation Grus, the crane. Now, in the fading afterglow of this blast, Hubble has captured NASA's first image of a surviving companion to a supernova. This picture is the most convincing proof that some supernovae are created in binary systems.
"We know that most massive stars are binary pairs," said Stuart Ryder of the Australian Astronomical Observatory (AAO) in Sydney, Australia and lead author of the study. "Many of these binary pairs interact and transmit gas from one star to another as their orbits bring them close to each other."
Supernova star's companion was not an uninvolved spectator at the blast. He took almost all the hydrogen out of the star shell of the doomed star, the region that transports energy from the star's core to its atmosphere. Millions of years before the primary star became a supernova, the companion's theft caused instability in the primary star, causing him to episodically burn down a cocoon and hydrogen gas shells before the disaster.
The Supernova SN 2001
How stripped Envelope supernovas lose this outer shell is not very clear. Originally, they were believed to come from individual stars with very fast winds that repel the outer shells. The problem was that astronomers, when they started looking for the primary stars that made up supernovae, could not find them for many supernovae with stripped sheaths.
"This was particularly bizarre because astronomers expected it to be the most massive and the brightest precursor stars," said team member Ori Fox of the Baltimore Space Telescope Science Institute. "In addition, the sheer number of stripped-hulled supernovas is larger than predicted." This fact led scientists to theorize that many of the primary stars appeared in lower-mass binary systems, and they set out to prove it.
Finding a binary companion after a supernova explosion is not an easy task. First, Hubble must be relatively close to Earth to see such a faint star. SN 2001ig and his companion are about at this limit. Within this range, not many supernovae are lost. More importantly, astronomers need to know the exact location through very accurate measurements.
In 2002, shortly after the explosion of the SN 2001ig, scientists using the Very Large Telescope (VLT) of the European Southern Observatory in Cerro Paranal determined the exact location of the Supernova, Chile. In 2004, they followed with the Gemini South Observatory in Cerro Pachón, Chile. This observation initially pointed to the existence of a surviving binary companion.
Ryder and his team were able to draw attention to this place 12 years later, when the Supernova flagged. With Hubble's exquisite resolution and ultra-violet capability, they were able to find and photograph the surviving companion – something only Hubble could do.
Before the supernova explosion, the orbit of the two stars lasted about a year. 19659003] When the primary star exploded, it had far less impact on the surviving companion than one might think. Imagine an avocado pit that represents the dense core of the companion star – embedded in a gelatin dessert – that represents the gaseous shell of the star. When a shock wave passes through, the gelatin may temporarily stretch and wobble, but the avocado pit remains intact.
In 2014, Fox and his team used Hubble to discover the companion of another Type IIb Supernova SN 1993J. However, they captured a spectrum, not a picture. The case SN 2001ig is the first time that a surviving companion has been photographed. "We were finally able to catch the stellar thief and confirmed our suspicion that you had to be there," Filippenko said.
Maybe even half of all stripped supernovas will be companions – the other half will lose their outer sheaths over stellar winds. Ryder and his team have the ultimate goal of determining exactly how many supernovae with undressed cases are with them.
Their next aim is to look at fully stripped Supernova casings, as opposed to SN 2001ig and SN 1993J, which were only about 90 percent stripped. These fully stripped-away supernovae do not have a strong impact interaction with gas in the surrounding stellar environment because their outer sheaths were lost long before the explosion. Without shock interaction they fade much faster. This means that the team only has to wait two or three years to search for surviving companions.
In the future, they also hope to use the James Webb Space Telescope to continue their search.