Active galactic nuclei are known to be the strongest compact steady sources of energy in the universe.
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.
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.
Asteroid 2023 BU just passed a few thousand kilometres from Earth. Here’s why that’s exciting – The Tribune India
Perth (Australia), January 28
There are hundreds of millions of asteroids in our Solar System, which means new asteroids are discovered quite frequently. It also means close encounters between asteroids and Earth are fairly common.
Some of these close encounters end up with the asteroid impacting Earth, occasionally with severe consequences.
A recently discovered asteroid, named 2023 BU, has made the news because today it passed very close to Earth.
Discovered on January 21 by amateur astronomer Gennadiy Borisov in Crimea, 2023 BU passed only about 3,600 km from the surface of Earth (near the southern tip of South America) six days later on January 27.
That distance is just slightly farther than the distance between Perth and Sydney and is only about 1 per cent the distance between Earth and our Moon.
The asteroid also passed through the region of space that contains a significant proportion of the human-made satellites orbiting Earth.
All this makes 2023 BU the fourth-closest known asteroid encounter with Earth, ignoring those that have impacted the planet or our atmosphere.
How does 2023 BU rate as an asteroid and a threat?
2023 BU is unremarkable, other than that it passed so close to Earth. The diameter of the asteroid is estimated to be just 4–8 metres, which is on the small end of the range of asteroid sizes.
There are likely hundreds of millions of such objects in our Solar System, and it is possible 2023 BU has come close to Earth many times before over the millennia. Until now, we have been oblivious to the fact.
In context, on average a 4-metre-diameter asteroid will impact Earth every year and an 8-metre-diameter asteroid every five years or so
Asteroids of this size pose little risk to life on Earth when they hit because they largely break up in the atmosphere. They produce spectacular fireballs, and some of the asteroids may make it to the ground as meteorites.
Now that 2023 BU has been discovered, its orbit around the Sun can be estimated and future visits to Earth predicted. It is estimated there is a 1 in 10,000 chance 2023 BU will impact Earth sometime between 2077 and 2123.
So, we have little to fear from 2023 BU or any of the many millions of similar objects in the Solar System.
Asteroids need to be greater than 25 metres in diameter to pose any significant risk to life in a collision with Earth; to challenge the existence of civilisation, they’d need to be at least a kilometre in diameter.
It is estimated there are fewer than 1,000 such asteroids in the Solar System and could impact Earth every 5,00,000 years. We know about more than 95 per cent of these objects.
Will there be more close asteroid passes?
2023 BU was the fourth closest pass by an asteroid ever recorded. The three closer passes were by very small asteroids discovered in 2020 and 2021 (2021 UA, 2020 QG and 2020 VT).
Asteroid 2023 BU and countless other asteroids have passed very close to Earth during the nearly five billion years of the Solar System’s existence, and this situation will continue into the future.
What has changed in recent years is our ability to detect asteroids of this size, such that any threats can be characterised. That an object roughly five metres in size can be detected many thousands of kilometres away by a very dedicated amateur astronomer shows that the technology for making significant astronomical discoveries is within reach of the general public. This is very exciting.
Amateurs and professionals can together continue to discover and categorise objects, so threat analyses can be done. Another very exciting recent development came last year, by the Double Asteroid Redirection Test (DART) mission, which successfully collided a spacecraft into an asteroid and changed its direction.
DART makes plausible the concept of redirecting an asteroid away from a collision course with Earth if a threat analysis identifies a serious risk with enough warning. (The Conversation)
An SUV-sized asteroid zoom by Earth in close shave flyby in this time-lapse video
Asteroid 2023 BU zipped past Earth Thursday night (Jan. 26) to the delight of amateur astronomers worldwide. For skywatchers without access to a telescope or those who had their view hampered by bad weather, luckily the Italy-based Virtual Telescope Project was there to observe the event and livestream the whole thing for free.
The Virtual Telescope is a robotic telescope operated by Italian amateur astronomer Gianluca Masi near Rome, Italy. As 2023 BU hurtled toward Earth, the telescope was able to track the rock through a gap in the clouds when it was about 13,670 miles (22,000 kilometers) from the closest point on Earth’s surface (about the altitude of the GPS navigation satellite constellation) and 22,990 miles (37,000 km) from the Virtual Telescope.
Masi, who shared an hour-long webcast of the observations on the Virtual Telescope website, wasn’t able to capture the closest approach as clouds rolled in, however. Nonetheless, the Virtual Telescope Project was able to get a good look at the car-sized rock, seen in time-lapse above.
The rock, discovered less than a week ago on Saturday (Jan. 21), passed above the southern tip of South America at 7:27 p.m. EST on Thursday Jan. 26 (0027 GMT on Jan. 27), at a distance of only 2,240 miles (3,600 km) at its closest point to Earth’s surface.
Only 11.5 to 28 feet wide (3.5 to 8.5 meters), 2023 BU posed no danger to the planet. If the trajectories of the two bodies had intersected, the asteroid would mostly have burned up in the atmosphere with only small fragments possibly falling to the ground as meteorites.
In the videos and images shared by Masi, the asteroid is seen as a small bright dot in the center of the frame, while the longer, brighter lines are the surrounding stars. In reality, of course, it was the asteroid that was moving with respect to Earth, traveling at a speed of 21,000 mph (33,800 km/h) with respect to Earth. As Masi’s computerized telescope tracked its positionthe rock appeared stationary in the images while rendering the stars as these moving streaks.
The gravitational kick that 2023 BU received during its encounter with Earth will alter the shape of its orbit around the sun. Previously, the space rock followed a rather circular orbit, completing one lap around the sun in 359 days. From now on, BU 2023 will travel through the inner solar system on a more elliptical path, venturing half way toward Mars at the farthest point of its orbit. This alteration will add 66 days to BU 2023’s orbital period.
The asteroid was discovered by famed Crimea-based astronomer and astrophotographer Gennadiy Borisov, the same man who in 2018 found the first interstellar comet, which now bears his name, Borisov.
Green comet zooming our way, last visited 50,000 years ago
A comet is streaking back our way after 50,000 years.
The dirty snowball last visited during Neanderthal times, according to NASA. It will come within 26 million miles (42 million kilometers) of Earth Wednesday before speeding away again, unlikely to return for millions of years.
So do look up, contrary to the title of the killer-comet movie “Don’t Look Up.”
Discovered less than a year ago, this harmless green comet already is visible in the northern night sky with binoculars and small telescopes, and possibly the naked eye in the darkest corners of the Northern Hemisphere. It’s expected to brighten as it draws closer and rises higher over the horizon through the end of January, best seen in the predawn hours. By Feb. 10, it will be near Mars, a good landmark.
Skygazers in the Southern Hemisphere will have to wait until next month for a glimpse.
While plenty of comets have graced the sky over the past year, “this one seems probably a little bit bigger and therefore a little bit brighter and it’s coming a little bit closer to the Earth’s orbit,” said NASA’s comet and asteroid-tracking guru, Paul Chodas.
Green from all the carbon in the gas cloud, or coma, surrounding the nucleus, this long-period comet was discovered last March by astronomers using the Zwicky Transient Facility, a wide field camera at Caltech’s Palomar Observatory. That explains its official, cumbersome name: comet C/2022 E3 (ZTF).
On Wednesday, it will hurtle between the orbits of Earth and Mars at a relative speed of 128,500 mph (207,000 kilometers). Its nucleus is thought to be about a mile (1.6 kilometers) across, with its tails extending millions of miles (kilometers).
The comet isn’t expected to be nearly as bright as Neowise in 2020, or Hale-Bopp and Hyakutake in the mid to late 1990s.
But “it will be bright by virtue of its close Earth passage … which allows scientists to do more experiments and the public to be able to see a beautiful comet,” University of Hawaii astronomer Karen Meech said in an email.
Scientists are confident in their orbital calculations putting the comet’s last swing through the solar system‘s planetary neighborhood at 50,000 years ago. But they don’t know how close it came to Earth or whether it was even visible to the Neanderthals, said Chodas, director of the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory in California.
When it returns, though, is tougher to judge.
Every time the comet skirts the sun and planets, their gravitational tugs alter the iceball’s path ever so slightly, leading to major course changes over time. Another wild card: jets of dust and gas streaming off the comet as it heats up near the sun.
“We don’t really know exactly how much they are pushing this comet around,” Chodas said.
The comet—a time capsule from the emerging solar system 4.5 billion years ago—came from what’s known as the Oort Cloud well beyond Pluto. This deep-freeze haven for comets is believed to stretch more than one-quarter of the way to the next star.
While comet ZTF originated in our solar system, we can’t be sure it will stay there, Chodas said. If it gets booted out of the solar system, it will never return, he added.
Don’t fret if you miss it.
“In the comet business, you just wait for the next one because there are dozens of these,” Chodas said. “And the next one might be bigger, might be brighter, might be closer.”
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