Supernovae are comparatively uncommon. It won’t look like it, however that’s as a result of they’re so shiny we are able to see them in different galaxies an important distance away. The truth is, in 2022, astronomers noticed a supernova over 10 billion light-years away.
Any time astronomers spot a supernova, it’s a chance to study extra about these uncommon, cataclysmic explosions. It’s particularly worthwhile if astronomers can get a very good have a look at the progenitor star earlier than it explodes.
We all know what forms of stars explode as core-collapse supernovae: huge ones. However we don’t know which star will explode when, so we don’t know the place to look to see the progenitor. The authors of latest analysis put this succinctly once they write, “Acquiring spectroscopic observations of the progenitors of core-collapse supernovae is usually unfeasible attributable to an inherent lack of understanding as to which stars will go supernova and when they’ll explode.”
That quote comes from a brand new analysis letter titled “Spectroscopic observations of progenitor activity 100 days before a Type Ibn supernova.” The letter has been submitted to the journal Astronomy and Astrophysics and is presently in pre-press. The lead writer is Seán Brennan from the Division of Astronomy at Stockholm College.
Astronomers continue to learn extra about supernovae progenitors. They’re discovering that supernova progenitors can exhibit highly effective outbursts within the weeks, months, and even years earlier than they explode. Astronomers maintain getting higher and higher instruments to identify these outbursts, and typically they get fortunate.
In April of 2023, a large star exploded in NGC 4388, a spiral galaxy about 57 million light-years away. The Zwicky Transient Facility (ZTF) noticed it, and the supernova known as SN 2023fyq. SN 2023fyq is a uncommon kind of supernova known as a Sort Ibn. They present a scarcity of hydrogen strains and slender He I emission strains of their spectra. Astronomers assume that these traits come from the SN interacting with hydrogen-poor, helium-rich circumstellar materials (CSM.)
Astronomers solely know of some of all these SN, so their progenitors are poorly understood. Previous to its explosion, the ZTF additionally noticed the precursor exercise, offering a window into these mysterious progenitors.
“This Letter presents spectral and photometric observations of the progenitor of a Sort Ibn SN a number of months earlier than core-collapse, in addition to SN 2023fyq itself,” the researchers write. The observations come from a number of telescopes and observatories, together with the Keck 10m telescope, the Palomar 200-inch telescope, and the Gemini North 8m telescope.
The researchers discovered that the progenitor’s luminosity elevated exponentially through the 150 days main as much as the explosion. In addition they discovered that the radius of the photosphere remained nearly fixed throughout the identical time. The pre-supernova spectra additionally “reveal a posh evolving He I profile.”
The He I profile may very well be a clue to among the progenitor star’s exercise. There are related He I emissions in each the progenitor and the SN. “This is able to imply that the uneven materials liable for this emission was not destroyed within the SN explosion,” the authors clarify. “SN ejecta interacting with uneven circumstellar materials (CSM) has been used to elucidate irregular emission line profiles.” We’re getting deep into the weeds right here, nevertheless it’s vital. “… SN 2023fyq supplies the primary clear spectroscopic proof of uneven construction previous to core-collapse.”
It’s potential that among the options within the spectroscopy are brought on by circumstellar materials (CSM). “Some mechanisms trigger the progenitor to be surrounded by a dense CSM,” the authors clarify, “and will result in shock dissipation and emission of radiation within the optically thick CSM.” In that case, diffusion may clarify the sunshine curve’s common rise. “This additionally explains the roughly fixed radius and the slowly rising efficient temperature,” they write.
“These observations of SN 2023fyq and the ultimate moments of the progenitor spotlight that the progenitors to CCSNe can bear some excessive instabilities shortly earlier than their closing demise,” the authors write.
It shouldn’t shock anybody {that a} progenitor exhibited some excessive instabilities earlier than exploding as a supernova. It could be very unusual if a large star abruptly exploded with no lead-up. Solely huge stars explode as supernovae, and it occurs when the star’s outward fusion strain is inadequate to counteract the star’s personal gravity. The star collapses in on itself and explodes. It is a cataclysmic occasion, and there are certain to be shock waves travelling by the star, in addition to different interactions. There are certain to be “excessive instabilities,” because the authors name them.
However what precisely does this inform us?
That is only a analysis letter, and the authors are presenting their outcomes to the astronomical neighborhood. They will present the weird exercise evident in spectroscopic observations, however they’ll’t inform us precisely what it means but. But it surely does present that we’re capable of spot supernova progenitors, an enormous step in understanding core-collapse supernovae.
“Progenitor evaluation usually happens after the star has been destroyed by looking by archival pictures and measuring the photometric properties of the assumed progenitor,” the researchers write of their letter. “Though this space of transient astronomy is in its infancy, the repercussions of detecting precursor exercise are immense, highlighting that the progenitor is just not in an equilibrium state and will
not be represented properly by normal stellar evolutionary fashions.”
We’re taking a look at an SN progenitor after we have a look at Betelgeuse; astronomers simply don’t know the way lengthy it’ll be till the star explodes. But it surely seems to have belched plasma that created a mud cloud that briefly dimmed the star a few years in the past. Is that behaviour indicative of how different progenitors behave?
Astronomers want to look at extra supernova progenitors of various sorts earlier than they’ll reply their questions. As soon as they’ve extra knowledge, they’ll construct fashions of how supernova progenitors behave main as much as the explosion. Then, they’ll observe much more SN and check that knowledge in opposition to their fashions. Then, they’ll enhance their fashions some extra.
Finally, they’ll have solutions.
