Within our galaxy, there are thousands of stars that orbit the center of the Milky Way at high velocities. On occasion, some of them pick up so much speed that they break free of our galaxy and become intergalactic objects. Because of the extreme dynamical and astrophysical processes involved, astronomers are most interested in studying these stars – especially those that are able to achieve escape velocity and leave our galaxy.
An artist’s conception of a hypervelocity star that has escaped the Milky Way. Credit: NASA
In terms of astrophysical studies, high-velocity stars are a relatively recent discovery. The first was observed in 2005, and in the subsequent 15 years, over 550 have been discovered by multiple observatories. From these, astronomers have been able to deduce four subclasses of high-velocity stars, which include: hypervelocity stars, runaway stars, hyper-runaway stars, and fast halo stars.
This latest discovery is especially significant then because it effectively doubles the number of known high-velocity stars, which are quite rare in our galaxy. “The 591 high-velocity stars discovered this time doubled the total number previously discovered, bringing the current total number exceeding 1,000,” said Dr. Li.
Hypervelocity stars (HVS), the fastest of the bunch, are especially interesting because they have achieved relativistic speeds (a fraction of the speed of light). In fact, astronomers have estimated that with the right kind of gravitational acceleration, hypervelocity stars can reach 1/10th to 1/3rd the speed of light – roughly 30,000 to 100,000 km/s (18,640 to 62,130 mi/s).
It is these stars that have the escape velocity needed to leave the Milky Way. Said Prof. LU Youjun from NAOC, a co-author of this paper:
“Though rare in the Milky Way, high-velocity stars, with unique kinematics, can provide deep insight into a wide range of Galactic science, from the central supermassive black hole to distant Galactic halo.”
The positions and reconstructed orbits of 20 high-velocity stars, represented on top of an artistic view of the Milky Way. Credit: ESA/Marchetti et al. 2018/NASA/ESA/Hubble
“Rare” is certainly an apt description. According to previous estimates made by astrophysicists, there are likely to be just 1000 HVS in our galaxy (that’s 0.0000005 % of the galactic population). But given their speed and the vast distances they travel, tracking these stars and creating a database of their movements could tell us a great deal about a number of cosmic mysteries.
For the sake of their study, the international team relied in part on data provided by LAMOST. In addition to being the largest optical telescope in China, LAMOST has the highest spectral acquisition rate of any telescope in the world and can observe about 4,000 celestial objects in a single exposure. Since it began conducting surveys in 2012, it has established the world’s largest spectra database.
In addition, the team relied on astrometric measurements performed by the Gaia Observatory, which was launched by the European Space Agency (ESA) in 2013. Since then, it has gathered information on the location, proper motion, and velocity of over 1.3 billion celestial objects, making it the largest astrometric database in the world. Both observatories and their massive databases have been invaluable in the detection and study of HVS.
Based on the motion and composition of the objects they observed, the research team identified 591 HVS that originated in the Milky Way’s inner halo. “Their low metallicities indicate that the bulk of the stellar halo formed as a consequence of the accretion and tidal disruption of dwarf galaxies,” said co-author Prof. Zhao Gang of the CAS School of Astronomy and Space Science.
One of the greatest takeaways from this study the way it demonstrates how combining multiple large surveys can lead to the discovery of rare objects. In the future, astronomers will be able to draw from even larger databases containing survey data provided by next-generation instruments. This data will be especially useful in the study of Dark Matter, the mysterious mass that constitutes 27% of the mass-energy density of the Universe.
By tracking the movement of HVS, astrophysicists will be able to better constrain the shape of the Milky Way’s dark matter halo. In addition, they could tell us a great deal about the formation and evolution of the Milky Way itself, as HVS are believed to be the result of galactic mergers and other extreme gravitational forces (i.e. supermassive holes). Having more to study could therefore help astronomers create a history of past galactic mergers.
It has also been ventured that HVS could allow astrophysicists to accurately constrain the mass of our galaxy, something that remains unresolved. On top of all that, previous research has indicated that HVS can carry their planetary systems with them, which could be one of the ways that life is spread throughout the cosmos (intergalactic panspermia).
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.
