An worldwide group of astronomers led by Benjamin Thomas of The University of Texas at Austin has used observations from the Hobby-Eberly Telescope (HET) on the college’s McDonald Observatory to unlock a puzzling thriller a couple of stellar explosion found a number of years in the past and evolving even now. The outcomes, revealed in in the present day’s challenge of The Astrophysical Journal, will assist astronomers higher perceive the method of how huge stars dwell and die.
When an exploding star is first detected, astronomers all over the world start to observe it with telescopes as the sunshine it provides off adjustments quickly over time. They see the sunshine from a supernova get brighter, finally peak, after which begin to dim. By noting the occasions of those peaks and valleys within the gentle’s brightness, referred to as a “light curve,” in addition to the attribute wavelengths of sunshine emitted at completely different occasions, they’ll deduce the bodily traits of the system.
“I think what’s really cool about this kind of science is that we’re looking at the emission that’s coming from matter that’s been cast off from the progenitor system before it exploded as a supernova,” Thomas stated. “And so this makes a sort of time machine.”
In the case of supernova 2014C, the progenitor was a binary star, a system wherein two stars have been orbiting one another. The extra huge star advanced extra shortly, expanded, and misplaced its outer blanket of hydrogen to the companion star. The first star’s internal core continued burning lighter chemical components into heavier ones, till it ran out of gas. When that occurred, the outward strain from the core that had held up the star’s nice weight dropped. The star’s core collapsed, triggering a big explosion.
This makes it a kind of supernova astronomers name a “Type Ib.” In explicit, Type Ib supernovae are characterised by not displaying any hydrogen of their ejected materials, at the least at first.
Thomas and his group have been following SN 2014C from telescopes at McDonald Observatory since its discovery that yr. Many different groups all over the world even have studied it with telescopes on the bottom and in area, and in several types of gentle, together with radio waves from the ground-based Very Large Array, infrared gentle, and X-rays from the space-based Chandra Observatory.
But the research of SN 2014C from all the varied telescopes didn’t add up right into a cohesive image of how astronomers thought a Type Ib supernova ought to behave.
For one factor, the optical signature from the Hobby-Eberly Telescope (HET) confirmed SN 2014C contained hydrogen — a shocking discovering that additionally was found independently by one other group utilizing a distinct telescope.
“For a Type Ib supernova to begin showing hydrogen is completely weird,” Thomas stated. “There’s just a handful of events that have been shown to be similar.”
For a second factor, the optical brightness (gentle curve) of that hydrogen was behaving surprisingly.
Most of the sunshine curves from SN 2014C — radio, infrared, and X-rays — adopted the anticipated sample: they acquired brighter, peaked, and began to fall. But the optical gentle from the hydrogen stayed regular.
“The mystery that we’ve wrestled with has been ‘How do we fit our Texas HET observations of hydrogen and its characteristics into that [Type Ib] picture?’,” stated UT Austin professor and group member J. Craig Wheeler.
The downside, the group realized, was that earlier fashions of this method assumed that the supernova had exploded and despatched out its shockwave in a spherical method. The knowledge from HET confirmed that this speculation was not possible — one thing else should have occurred.
“It just would not fit into a spherically symmetric picture,” Wheeler stated.
The group proposes a mannequin the place the hydrogen envelopes of the 2 stars within the progenitor binary system merged to type a “common-envelope configuration,” the place each have been contained inside a single envelope of gasoline. The pair then expelled that envelope in an increasing, disk-like construction surrounding the 2 stars. When one of many stars exploded, its fast-moving ejecta collided with the slow-moving disk, and likewise slid alongside the disk floor at a “boundary layer” of intermediate velocity.
The group means that this boundary layer is the origin of the hydrogen they detected after which studied for seven years with HET.
Thus the HET knowledge turned out to be the important thing that unlocked the thriller of supernova SN 2014C.
“In a broad sense, the question of how massive stars lose their mass is the big scientific question we were pursuing,” Wheeler stated. “How a lot mass? Where is it? When was it ejected? By what bodily course of? Those have been the macro questions we have been going after.
“And 2014C just turned out to be a really important single event that’s illustrating the process,” Wheeler stated.