By Looking Back Through Hubble Data, Astronomers Have Identified six Massive Stars Before They Exploded as Core-Collapse Supernovae | Canada News Media
The venerable Hubble Space Telescopehas given us so much during the history of its service (32 years, 7 months, 6 days, and counting!) Even after all these years, the versatile and sophisticated observatory is still pulling its weight alongside more recent addition, like the James Webb Space Telescope (JWST) and other members of NASA’s Great Observatories family. In addition to how it is still conducting observation campaigns, astronomers and astrophysicists are combing through the volumes of data Hubble accumulated over the years to find even more hidden gems.
A team led by Caltech’s recently made some very interesting finds in the Hubble archives, where they observed the sites of six supernovae to learn more about their progenitor stars. Their observations were part of the Hubble Space Telescope Snapshot program, where astronomers use HST images to chart the life cycle and evolution of stars, galaxies, and other celestial objects. From this, they were able to place constraints on the size, mass, and other key characteristics of the progenitor stars and what they experienced before experiencing core collapse.
The team was led by Dr. Schuyler D. Van Dyk, a senior research scientist with Caltech’s Infrared Processing and Analysis Center (IPAC). His teammates included researchers from the University of California, Berkeley, the Space Telescope Science Institute, the University of Arizona’s Steward Observatory, the University of Hawai’i’s Institute for Astronomy, and the School of Physics and Astronomy at the University of Minnesota. Their findings were published in a paper titled “The disappearance of six supernova progenitors” that will appear in the Monthly Notices of the Royal Astronomical Society.
The Hubble Ultra Deep Field seen in ultraviolet, visible, and infrared light. Image Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)
As they indicate in their paper, the targets of their study were all nearby core-collapse supernovae (SNe) that Hubble imaged at high spatial resolutions. The images were part of the Hubble Snapshot program, created by the Space Telescope Science Institute (STScI) to provide a large sample of images for various targets. Every target is observed in a single orbit of Hubble around the Earth between other observation programs, allowing a degree of flexibility that is not possible with other observatories.
For their study, Van Dyk and his colleagues examined images of six extragalactic supernovae before and after they exploded – designated SN 2012A, SN 2013ej, SN 2016gkg, SN 2017eaw, SN 2018zd, and SN 2018aoq. With extragalactic targets, astronomers have difficulty knowing if the stars they identified were progenitors to the supernova, given the distance involved. As Van Dyk to Universe Today via email, the only way to be sure is to wait for the supernova to dim, then confirm that the progenitor star has disappeared:
“Since the supernova explosion is so luminous, we have to wait a number of years until it has faded enough that it is less luminous than was the progenitor. In a few of the cases we show in our paper, there is little question that the star that was there pre-explosion is now gone. In the other cases, we’re reasonably sure, but the supernova is still detectable and is just faint enough for us to infer that the progenitor has vanished. “
In a previous study, Van Dyk and several colleagues who were co-authors of this study investigated another supernova (iPTF13bvn) whose progenitor star disappeared. In this case, the research team relied on data obtained by Hubble of the SN site – as part of the Ultraviolet Ultra Deep Field (UVUDF) campaign – roughly 740 days after the star exploded. In 2013, Van Dyk led a study that used images from an earlier Snapshot program to confirm that the progenitor of SN 2011dh in the Whirlpool Galaxy (Messier 51) had disappeared.
The Whirlpool Galaxy (Spiral Galaxy M51, NGC 5194), a classic spiral galaxy located in the Canes Venatici constellation, and its companion NGC 5195. Credit: NASA/ESA
These and other papers over the years have shown that progenitor candidates can be directly identified from pre-explosion images. In this most recent study, Van Dyk and his colleagues observed supernovae in the later stages of their evolution to learn what mechanisms are powering them. In many cases, the mechanism is the decay of radioactive nuclei (in particular, radioactive nickel, cobalt, and iron) that were synthesized by the enormous energy of the explosion. But as he explained, they suspected that other mechanisms might be involved:
“However, we have indications that some supernovae inevitably have additional power sources — one possibility is that the light of the supernova has been scattered by interstellar dust immediate to the explosion, in the form of a ‘light echo’; another more likely possibility is that the shockwave associated with the explosion is interacting with gas that was deposited around the progenitor star by the star itself during the course of the star’s life, in the form of wind or outburst, that is, circumstellar matter. The ejecta from the explosion moving through and interacting with this circumstellar matter can result in luminous energy that can persist for years, even for decades.”
In short, the team was trying to estimate how many of the supernovae they observed evolved through radioactive decay versus more exotic powering mechanisms. Their results showed that SN 2012A, SN 2018zd, and SN 2018aoq had faded to the point where they were no longer detectable in the Hubble Snapshot images, whereas SN 2013ej, SN 2016gkg, and SN 2017eaw had faded just enough. Therefore, they could infer in all six cases that the progenitors had disappeared. However, not all were the result of a single massive star undergoing core collapse.
In the case of SN 2016gkg, the images acquired by Hubble’s Wide Field Camera 3 (WFC3) were of much higher spatial resolution and sensitivity than the images of the host galaxy, previously taken by the now-retired WFC2. This allowed them to theorize that SN 2016gkg was not the result of a single core-collapse supernova but a progenitor star interacting with a neighboring star. Said Van Dyk:
“So, in the old image, the progenitor looked like one “star,” whereas in the new images, we could see that the progenitor had to have been spatially distinct from the neighboring star. Therefore, we were able to obtain a better estimate of the progenitor’s luminosity and color, now uncontaminated by the neighbor, and from that, we were able to make some new inferences about the overall properties of the progenitor, or, in this case, progenitor system, since we characterized the new results using existing models of binary star systems.”
Artist’s impression of a supernova remnant. Credit: ESA/Hubble
Specifically, they determined that the progenitor belonged to the class of “stripped-envelope” supernovae (SESNe), in which the outer hydrogen H-rich envelope of the progenitor star has been significantly or entirely removed. They further estimated that the progenitor was the primary and its companion was likely a main sequence star. They even placed constraints on their respective masses before the explosion (4.6 and 17–20.5 solar masses, respectively).
After consulting images taken around the same time by another Snapshot program, they also noticed something interesting about SN 2017eaw. These images indicated that this supernova was especially luminous in the UV band (an “ultraviolet excess”). By combining these images with their data, Va Dyk and his team speculated that SN 2017eaw had an excess of light in the UV at the time it was observed, which was likely caused by interaction between the supernova shock and the circumstellar medium around that progenitor.
The team also noted that the dust created by a supernova explosion is a complicating factor due to how it cools as it expands outward. This dust, said Van Dyk, can obscure light from distant sources and lead to complications with the observations:
“The caveat here, then, is that the star that we saw pre-explosion might not be the progenitor at all, for instance and — again, because of the distances to the host galaxies — that star is within fractions of a pixel of the actual progenitor (physically, in the immediate neighborhood of the progenitor), such that, if the supernova has made dust, that dust is effectively blanketing both the supernova and that neighboring star. This is possible, but not inordinately likely. And it becomes a harder argument to make in those few cases where nothing is seen at the supernova position years later — as we point out in the paper, that would require enormous amounts of dust, which is likely physically not possible.”
Tracing the origins of supernovae is one of the many ways astronomers can learn more about the life cycle of stars. With improved instruments, data collection, and flexibility, they are able to reveal more about how our Universe evolved and will continue to change over time.
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
