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An Analysis of an Active Galactic Nucleus

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Active galactic nuclei are known to be the strongest compact steady sources of energy in the universe. 

An artist’s impression of what the dust around an active galactic nucleus might look like seen from a light year away. Image Credit: Peter Z. Harrington

The existence of the brightest active galactic nuclei has long been known to far outshine the integrated light of the billions of stars present in their host galaxies.

A new study performed shows that researchers have considerably undervalued the energy output of such objects by not acknowledging the extent to which their light has been dimmed by dust.

When there are intervening small particles along our line of sight, this makes things behind them look dimmer. We see this at sunset on any clear day when the sun looks fainter.

Martin Gaskell, Research Associate, Astronomy and Astrophysics, University of California-Santa Cruz

Gaskell is the lead author of a study on the new findings reported in the Monthly Notices of the Royal Astronomical Society on January 16th, 2022.

Although the chances of dust dimming the light from active galactic nuclei have been identified for a while, the amount has been debated and was frequently believed to be negligible, stated Gaskell.

We have shown that this is not the case and that the far ultraviolet light of a typical active galactic nucleus is dimmed by a large factor,” Gaskell said.

This conclusion was reached by the group by studying the reddening effect of dust on the light coming from one of the most well-studied active galactic nuclei, called NGC 5548. Similar to how the Earth’s atmosphere makes the sun emerge redder as well as dimmer at sunset, in the same way, the dust present in the active galactic nuclei also makes them appear redder than they really are. The amount of reddening corresponds to the amount of dimming.

Researchers measure the colors of something by quantifying the ratios of the intensity of its light at various wavelengths. While we know what a non-reddened sun looks like, there has been much discussion over the non-reddened emissions coming from active galactic nuclei.

In the new study of NGC 5548, the University of California-Santa Cruz (UCSC) scientists made use of seven indicators of the amount of dust and discovered them all to be in reasonable agreement. Moreover, the NGC 5548’s dimming as a result of dust was shown to be large, over ten times the dimming caused by dust seen in the Milky Way.

The good agreement between the different indicators of the amount of reddening was a pleasant surprise. It strongly supports simple theories of emission from active galactic nuclei. Exotic explanations of colors are not needed. This makes life simpler for researchers and is speeding up our understanding of what happens as black holes swallow material.

Martin Gaskell, Research Associate, Astronomy and Astrophysics, University of California-Santa Cruz

The NGC 5548’s colors are normal for other active galactic nuclei, stated Gaskell, which has extensive implications.

The outcomes suggest that in the ultraviolet, where the majority of the energy has been radiated, a normal active galactic nucleus is putting out an order of magnitude more energy compared to what was previously thought, stated Gaskell.

Gaskell stated that one more implication is that active galactic nuclei are extremely similar, and what have so far been thought to be significant fundamental variations between them are really just the impacts of various amounts of reddening dust.

The co-authors of the Gaskell—Frances Anderson (now at Harvey Mudd College), Sufia Birmingham (now at Princeton University), and Samhita Ghosh (currently at UC Berkeley)—worked on this project.

Journal Reference

Gaskell, C. M., et al. (2022) Estimating reddening of the continuum and broad-line region of active galactic nuclei: the mean reddening of NGC 5548 and the size of the accretion disc Get access Arrow. Monthly Notices of the Royal Astronomical Society. doi.org/10.1093/mnras/stac3333.

Source: https://www.ucsc.edu/

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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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