Astronomers Caught Betelgeuse Just Before it Started Dimming and Might Have Seen a Pressure Wave Rippling Through its Atmosphere - Universe Today | Canada News Media
A couple of years ago, Betelgeuse generated much interest when it started dimming. That caught the attention of astronomers worldwide, who tried to understand what was happening. Was it about to go supernova?
Evidence showed that dust was the most likely culprit for the red supergiant’s dimming, though there are still questions. A new study shows that the star was behaving strangely just before the dimming.
The optical dimming that Betelgeuse—or Alpha Orionis—exhibited in late 2019 and early 2020 was unprecedented. Betelgeuse often undergoes periodic optical dimming, which happens in timescales of ~300-500 days and ~2000 days. But the Great Dimming, as it came to be known—when the star dimmed to about two-thirds of its normal brightness— was the faintest that the star had become in almost 200 years of observations.
Researchers got to work generating possible explanations for the dimming. Some hypothesized that dust caused the dimming, others hypothesized that a reduction in photosphere temperature caused it, and some thought both played a role.
Astronomers continued studying it, and evidence showed that temperature decrease alone couldn’t be the culprit. Episodic mass loss was proposed as the cause, paired with a rise in large grain dust in the line of sight. Others argued that large inhomogeneities in the photosphere caused the dimming. Another suggested a critical shift in Betelgeuse’s pulsation dynamics caused the Great Dimming. If feedback from UT readers is any indication, there’s still confusion around the cause of the dimming event.
Betelgeuse, as seen by the Hubble Space Telescope. Credit: NASA
But there were really two dimming events, and that’s helped create some of the confusion. The scientific community has settled on dust as the cause of the first dimming. “We know the first dimming event involved a dust cloud,” said Dr. Meridith Joyce from The Australian National University in 2020.
According to Dr. Joyce, the second dimming event had a different cause: “We found the second smaller event was likely due to the pulsations of the star.”
Now a new paper presents observations of Betelgeuse just before the Great Dimming. Its title is “SPATIALLY RESOLVED OBSERVATIONS OF BETELGEUSE AT ?7 MM AND ?1.3 CM JUST PRIOR TO THE GREAT DIMMING.” The Astrophysical Journal will publish it, but for now, it’s available on the pre-press site arxiv.org. The authors are Dr. Lynn D. Matthews of MIT’s Haystack Observatory and Andrea Dupree from the Harvard and Smithsonian Center for Astrophysics. The paper is based on observations of Betelgeuse with the Karl G. Jansky Very Large Array.
“Our measurements suggest recent changes in the temperature and density structure of the atmosphere,” the authors write. The star’s photosphere “… is ~20% dimmer than in previously published observing epochs between 1996–2004.” This is … lower than previously reported temperatures at comparable radii and >1200 K lower than predicted by previous semi-empirical models of the atmosphere.”
Betelgeuse is known for pulsating, as it swells and shrinks symmetrically. These are Hubble images of the star from 1998 and 1999. Image Credit: NASA/ESA/Hubble
The researchers also found that the measured brightness temperature was cooler than expected and that there were “… no obvious signatures of giant convective cells or other surface features.” The star’s brightness profile was also more complex than a uniform elliptical disk (A uniform elliptical disk is a tool astrophysicists use to characterize the mean properties of a star.) Their observations were from about six weeks before ultraviolet measurements found increases in electron density in Betelgeuse’s southern hemisphere, coupled with a large-scale outflow.
So what does all that mean?
“We discuss possible scenarios linking these events with the observed radio properties of the star, including the passage of a strong shock wave.”
Researchers in the astrophysical community have postulated that a shock wave could’ve caused the Great Dimming. A 2021 paper found that Betelgeuse’s photosphere experienced successive shock waves in February 2018 and January 2019, with the initial shock amplifying the second one. Other research showed that a shock wave passed through the southwestern portion of Betelgeuse’s chromosphere between 2019 September and November. Since the photosphere is under the chromosphere, it’s reasonable to think that the two shock waves are related.
This diagram of a star’s layers shows how the photosphere is below the chromosphere. The photosphere is the lowest layer of a star’s atmosphere and the lowest observable layer. Image Credit: ESA
The researchers say they can’t conclude that their observations are directly responsible for the Great Dimming, even though their data suggests “… recent changes in the density and/or temperature structure of the atmosphere…” But a large-amplitude shock or pressure wave passing through Betelgeuse’s atmosphere could cause changes in density and temperature.
The authors are cautious and inconclusive, but they do point out that the pressure wave they observed could’ve caused Betelgeuse’s Great Dimming. “Such an event may be linked to a largescale mass ejection from the star that has been postulated as an explanation for the steep decline in optical magnitude associated with the Great Dimming.”
There’s no question that Betelgeuse will explode as a Type IIP supernova, likely in the next 100,000 years or so. It’s the 10th brightest star in the night sky and is giving astronomers an opportunity to study intensely the behaviour of a star as it approaches its cataclysmic end.
The familiar constellation of Orion. Orion’s Belt can be clearly seen, as well as Betelgeuse (red star in the upper left corner) and Rigel (bright blue star in the lower right corner). Credit: NASA Astronomy Picture of the Day Collection NASA
This study won’t be the final word on Betelgeuse and its dynamic behaviour. The star is still up there, anchoring the Orion the Hunter’s right shoulder. Generations and generations of astronomers are bound to keep watching it.
If humanity lasts long enough, our distant descendants will get to watch it explode.
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.
