Astronomers may have for the first time detected and measured the mass of an isolated stellar-mass black hole, a new study finds.
Previous research suggested that when giant stars more than 20 times the mass reach the end of their lives, they usually die in catastrophic explosions known as supernovas, and their dense cores are expected to collapse to become black holes.
Stars big enough to create black holes are estimated to make up about one out of a thousand stars, suggesting that in the Milky Way, “there should be about 100 million stellar-mass black holes,” study lead author Kailash Sahu, an astrophysicist at the Space Telescope Science Institute in Baltimore, told Space.com. (Stellar-mass black holes are up to a few times the sun‘s mass, as opposed to supermassive black holes millions of billions of solar masses large.)
Until now, all stellar-mass black holes detected to date have existed in binary systems with partners such as neutron stars. In contrast, the majority of the Milky Way’s stellar-mass black holes should be singletons, Sahu said.
However, “nobody has ever been able to find an isolated black hole,” Sahu said. As their name suggests, black holes absorb any light that falls into them, making them difficult to detect against the dark of space. Black holes are easier to detect in binary systems because their interactions with their partners can generate light or gravitational waves whose properties signal a black hole’s presence. In contrast, isolated black holes lack such partners to help reveal their existence.
Now, with the help of NASA’s Hubble Space Telescope, scientists have discovered an isolated stellar-mass black hole about 5,150 light-years away from Earth, in the direction of the bulge in the center of the Milky Way.
“We now know that isolated black holes exist,” Sahu said. “And they have masses similar to the black holes found in binaries. And there must be lots of them out there.”
The key behind this discovery is how powerful gravitational fields, such as those belonging to black holes, warp the fabric of space and time. As such, they can act like magnifying glasses, a phenomenon known as “gravitational lensing.”
“If one can detect and measure the bending of light caused by these massive objects, it’s possible to detect them and measure their masses,” Sahu said.
A number of ground-based survey programs monitor millions of stars every night to detect gravitational lensing events “where a star slowly brightens and fades over days or months,” Sahu said. “This microlensing phenomenon is caused by an intervening object, which can be a star or a white dwarf or a neutron star or a black hole or so on. The survey programs typically detect about 2,000 microlensing events per year. A small number of them are expected to be caused by black holes.”
The greater the mass of a gravitational lensing object, the longer the resulting brightening. Since a black hole is expected to be massive, its microlensing event is expected to have a long duration. “Also, a black hole is expected to be dark,” Sahu explained. “So we use these two as our main criteria — the event should have a long duration, and the lens should not be emitting any light.”
However, small-mass stars that move slowly in the sky may also look relatively dark and generate long-duration gravitational lensing events. One way to distinguish an isolated black hole from a small-mass star is the fact that a black hole will deflect the light from background stars “enough that it can be measured with Hubble,” Sahu said. “If the Hubble observations show large deflection but no light from the lens, then it would be a black hole.”
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By combining Hubble observations with ground telescope data, the scientists discovered a 270-day-long microlensing event, called MOA-2011-BLG-191/OGLE-2011-BLG-0462, which they said likely came from an isolated black hole.
“It took two years of planning followed by six years of observing with Hubble, but it was very satisfying to see the incredible results,” Sahu said. “It was immediately clear as daylight that it’s a black hole, there was nothing else that could cause the deflections we measured.”
The researchers estimated this isolated black hole was about 7.1 times the mass of the sun. They also found this black hole is traveling at a speed of about 100,000 mph (162,000 kph). This suggested this black hole may have received a kick from the supernova explosion that gave birth to it.
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.
