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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.

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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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SpaceX launch marks 300th successful booster landing – Phys.org

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Credit: Unsplash/CC0 Public Domain

SpaceX sent up the 30th launch from the Space Coast for the year on the evening of April 23, a mission that also featured the company’s 300th successful booster recovery.

A Falcon 9 rocket carrying 23 of SpaceX’s Starlink internet satellites blasted off at 6:17 p.m. Eastern time from Cape Canaveral Space Force Station’s Space Launch Complex 40.

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The first-stage booster set a milestone of the 300th time a Falcon 9 or Falcon Heavy booster made a successful recovery landing, and the 270th time SpaceX has reflown a booster.

This particular booster made its ninth trip to space, a resume that includes one human spaceflight, Crew-6. It made its latest recovery landing downrange on the droneship Just Read the Instructions in the Atlantic Ocean.

The company’s first successful booster recovery came in December 2015, and it has not had a failed booster landing since February 2021.

The current record holder for flights flew 11 days ago making its 20th trip off the .

SpaceX has been responsible for all but two of the launches this year from either Kennedy Space Center or Cape Canaveral with United Launch Alliance having launched the other two.

SpaceX could knock out more launches before the end of the month, putting the Space Coast on pace to hit more than 90 by the end of the year, but the rate of launches by SpaceX is also set to pick up for the remainder of the year with some turnaround times at the Cape’s SLC-40 coming in less than three days.

That could amp up frequency so the Space Coast could surpass 100 launches before the end of the year, with the majority coming from SpaceX. It hosted 72 launches in 2023.

More launches from ULA are on tap as well, though, including the May 6 launch atop an Atlas V rocket of the Boeing CST-100 Starliner with a pair of NASA astronauts to the International Space Station.

ULA is also preparing for the second launch ever of its new Vulcan Centaur rocket, which recently received its second Blue Origin BE-4 engine and is just waiting on the payload, Sierra Space’s Dream Chaser spacecraft, to make its way to the Space Coast.

Blue Origin has its own it wants to launch this year as well, with New Glenn making its debut as early as September, according to SLD 45’s range manifest.

2024 Orlando Sentinel. Distributed by Tribune Content Agency, LLC.

Citation:
SpaceX launch marks 300th successful booster landing (2024, April 24)
retrieved 24 April 2024
from https://phys.org/news/2024-04-spacex-300th-successful-booster.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

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Wildlife Wednesday: loons are suffering as water clarity diminishes – Canadian Geographic

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The common loon, that icon of northern wilderness, is under threat from climate change due to declining water clarity. Published earlier this month in the journal Ecology, a study conducted by biologists from Chapman University and Rensselaer Polytechnic Institute in the U.S. has demonstrated the first clear evidence of an effect of climate change on this species whose distinct call is so tied to the soundscape of Canada’s lakes and wetlands.

Through the course of their research, the scientists found that July rainfall results in reduced July water clarify in loon territories in Northern Wisconsin. In turn, this makes it difficult for adult loons to find and capture their prey — mainly small fish — underwater, meaning they are unable to meet their chicks’ metabolic needs. Undernourished, the chicks face higher mortality rates. The consistent foraging techniques used by loons across their range means this impact is likely echoed wherever they are found — from Alaska to Canada to Iceland.

The researchers used Landsat imagery to find that there has been a 25-year consistent decline in water clarity, and during this period, body weights of adult loon and chicks alike have also declined. With July being the month of most rapid growth in young loons, the study also pinpointed water clarity in July as being the greatest predictor of loon body weight. 

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One explanation for why heavier rainfall leads to reduced water clarity is the rain might carry dissolved organic matter into lakes from adjacent streams and shoreline areas. Lawn fertilizers, pet waste and septic system leaks may also be to blame.

The researchers, led by Chapman University professor Walter Piper, hope to use these insights to further conservation efforts for this bird Piper describes as both “so beloved and so poorly understood.”

Return of the king

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Giant prehistoric salmon had tusk-like teeth for defence, building nests

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The artwork and publicity materials showcasing a giant salmon that lived five million years ago were ready to go to promote a new exhibit, when the discovery of two fossilized skulls immediately changed what researchers knew about the fish.

Initial fossil discoveries of the 2.7-metre-long salmon in Oregon in the 1970s were incomplete and had led researchers to mistakenly suggest the fish had fang-like teeth.

It was dubbed the “sabre-toothed salmon” and became a kind of mascot for the Museum of Natural and Cultural History at the University of Oregon, says researcher Edward Davis.

But then came discovery of two skulls in 2014.

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Davis, a member of the team that found the skulls, says it wasn’t until they got back to the lab that he realized the significance of the discovery that has led to the renaming of the fish in a new, peer-reviewed study.

“There were these two skulls staring at me with sideways teeth,” says Davis, an associate professor in the department of earth sciences at the university.

In that position, the tusk-like teeth could not have been used for biting, he says.

“That was definitely a surprising moment,” says Davis, who serves as director of the Condon Fossil Collection at the university’s Museum of Natural and Cultural History.

“I realized that all of the artwork and all of the publicity materials and bumper stickers and buttons and T-shirts we had just made two months prior, for the new exhibit, were all out of date,” he says with a laugh.

Davis is co-author of the new study in the journal PLOS One, which renames the giant fish the “spike-toothed salmon.”

It says the salmon used the tusk-like spikes for building nests to spawn, and as defence mechanisms against predators and other salmon.

The salmon lived about five million years ago at a time when Earth was transitioning from warmer to relatively cooler conditions, Davis says.

It’s hard to know exactly why the relatives of today’s sockeye went extinct, but Davis says the cooler conditions would have affected the productivity of the Pacific Ocean and the amount of rain feeding rivers that served as their spawning areas.

Another co-author, Brian Sidlauskas, says a fish the size of the spike-toothed salmon must have been targeted by predators such as killer whales or sharks.

“I like to think … it’s almost like a sledgehammer, these salmon swinging their head back and forth in order to fend off things that might want to feast on them,” he says.

Sidlauskas says analysis by the lead author of the paper, Kerin Claeson, found both male and female salmon had the “multi-functional” spike-tooth feature.

“That’s part of our reason for hypothesizing that this tooth is multi-functional … It could easily be for digging out nests,” he says.

“Think about how big the (nest) would have to be for an animal of this size, and then carving it out in what’s probably pretty shallow water; and so having an extra digging tool attached to your head could be really useful.”

Sidlauskas says the giant salmon help researchers understand the boundaries of what’s possible with the evolution of salmon, but they also capture the human imagination and a sense of wonder about what’s possible on Earth.

“I think it helps us value a little more what we do still have, or I hope that it does. That animal is no longer with us, but it is a product of the same biosphere that sustains us.”

This report by The Canadian Press was first published April 24, 2024.

Brenna Owen, The Canadian Press

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