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White Dwarfs + Compact Objects – Trottier Institute for Research on Exoplanets

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Our Institute’s researchers study more than just exoplanets. In addition to planets and the stars they orbit, our scientists also look at “dead” stars. Sometimes called compact objects or stellar remnants, these are the objects leftover at the end of a star’s life, once it has used up all of its fuel.

Death of a star

The most common type of stellar remnant is a white dwarf, the final fate of more than 97% of the stars in our Galaxy. White dwarfs are created when a small-to-moderately-large sized star burns all of its nuclear fusion fuel, and its core contracts. The outer layers are blown away to create a beautiful planetary nebula, revealing the dense core which has become a white dwarf. Imagine an object with mass similar to our Sun, but compressed down to the size of the Earth. A teaspoon of white dwarf material would weigh as much as three African elephants! This will be the ultimate fate of our own star, the Sun.

An artist’s rendering of an exoplanet orbiting the pulsar PSR B1257+12. (Credit: NASA/JPL-Caltech)

Neutron stars are even more extreme stellar remnants. They are formed when very large stars run out of fuel. The process begins the same way as for white dwarfs, but in this case, there is too much mass and the contracting core squeezes past the white dwarf stage. The core squeezes down into a ball of pure neutrons.  They can have several times the mass of our Sun, but are only about as large as a city. These are the densest objects we know of, and a small handful of neutron star material on Earth would weigh as much as a mountain!

For the most massive stars, the collapse crushes even the ultra-dense ball of neutrons. These huge stars can turn into black holes when they exhaust their fuel. Black holes are extreme objects that have so much matter packed into such a tiny space that not even light goes fast enough to escape if it wanders too close.

Planets around dead stars?

What do these compact objects have to do with exoplanets? Since stellar remnants were once stars, they may have had planetary systems. They may have even retained their planets after their deaths. In fact, the first exoplanets ever discovered were not found around a regular star, but rather around a neutron star.

There is a special category of neutron stars called pulsars. They get this name because they rotate and pulse radio waves with incredible regularity, making pulsars some of the most stable clocks in the Universe. This regular pulse pattern can wobble slightly if other objects orbit the pulsar.  It was exactly this kind of pulsar wobble that revealed the very first confirmed exoplanet in 1992 around the pulsar PSR 1257+12. This discovery was made by Canadian astronomer Dale Frail (DRAO) and Polish astronomer Aleksander Wolszczan.

Polluted white dwarfs

An artist’s rendering of a destroyed comet around the white dwarf G29-38. (Credit: NASA/JPL-Caltech/GSFC)

White dwarfs provide a very different way of studying exoplanets. One important way that white dwarfs are different from regular stars is their high surface gravity. The gravity on the surface of a white dwarf would make a human weigh millions of kilograms! This causes heavier elements to sink rapidly, leaving a very clean and pure surface of mostly hydrogen and helium. As astronomers studied more white dwarfs, they discovered that some are “polluted” with heavier elements. The only way these heavy elements could be at the surface is if they were recently or continuously deposited there.

How could white dwarfs get polluted atmospheres? As a regular star nears the end of its life and eventually turns into a white dwarf, it can cause gravitational instabilities in its system. Objects such as planets, asteroids, and comets that may have been on stable orbits before the star died might now become unstable. If one of them falls too close to the white dwarf, it can easily be torn apart and form a disc of material that gets accreted onto the surface. Such polluted white dwarfs show us what these shredded objects were made of. This is different from measuring the composition of an exoplanet’s atmosphere, because polluted white dwarfs also reveal the planet’s crust and core materials, not just the atmospheric gasses.

No planets are yet known to exist around black holes, but that doesn’t mean it’s not possible. Researchers are currently looking for signs of planets in systems called x-ray binaries, where a black hole feeds off a stellar companion and emits strong x-rays.

White dwarfs and compact objects at iREx

Many of our iREx researchers are experts on these stellar remnants. Their expertise in these strange objects helps us to study exoplanets in unique ways. To learn more, we invite you to read their profiles:

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The body of a Ugandan Olympic athlete who was set on fire by her partner is received by family

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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.

Kenya’s high rates of violence against women have prompted marches by ordinary citizens in towns and cities this year.

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.

The Canadian Press. All rights reserved.

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The ancient jar smashed by a 4-year-old is back on display at an Israeli museum after repair

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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.”

The Canadian Press. All rights reserved.

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B.C. sets up a panel on bear deaths, will review conservation officer training

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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.

The Canadian Press. All rights reserved.

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