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We’re Living Next Door To A Cannibal Galaxy Whose Violent Past Has Been Revealed

A study of the small galaxies swallowed by our nearest large galactic neighbor has revealed something of how galaxies grow. In the process, it has hinted at something that, if true, would change the way we see the universe in profound ways.

All galaxies, including our own Milky Way, grow by consuming smaller ones. Inevitably, the nearest large galaxy to our own, M31, also known as Andromeda, has eaten many small neighbors. Our first insight into the nature of these events is useful because Andromeda and the Milky Way are on course to meet. That’s 4 billion years away, but it’s good to be prepared.

Dr Dougal Mackey of the Australian National University and Professor Geraint Lewis from the University of Sydney analyzed streams of stars within Andromeda’s halo and identified some as the remnants of galaxies, even gaining approximations of when this occurred. Rather than a steady process, they identified two bursts separated by billions of years. The galaxies in the two rounds arrived at right angles to each other and maintained that motion even after being pulled apart.

“We are cosmic archaeologists, except we are digging through the fossils of long-dead galaxies rather than human history,” Lewis said in a statement.

Mackey told IFLScience the consumed galaxies contained globular clusters, groups of stars bound so closely together that only the most powerful gravitational disruptions pull them apart.

Individual stars in Andromeda’s halo are usually too distant and faint for us to track their movements, but the clusters are a different matter, allowing the pair to identify in Nature the streams whose shared movements pin them as past galaxies.

“Once you get below a certain mass, galaxies don’t contain globular clusters,” Mackey said, so the smallest are currently untraceable. However, he added that the contribution of these to Andromeda’s growth was minor.

One day, Andromeda will swallow the Milky Way as well. However, Mackey acknowledged to IFLScience this will be a very different process. The galaxies Andromeda has eaten up until now have masses a tenth of its total at most, usually much smaller. The Milky Way, on the other hand, is at least half Andromeda’s size.

The merger of the two will destroy the spiral structure of each, creating an egg-like elliptical galaxy. By then, the Sun will have burned the Earth beyond recognition, but if humanity somehow survives elsewhere, consequences will be limited. Our view of the night sky will change utterly, but the space between the stars is so great that even when stars from Andromeda become mixed among our nearest neighbors, it is unlikely any will pass close enough to disrupt orbits within the inner solar system.

One feature of the pair’s work is still tentative but could turn out to be awe-inspiring. Around a decade ago astronomers noticed a curious pattern in the dwarf galaxies that surround Andromeda. Around half these galaxies orbit in a specific plane, something astronomers had not expected and struggled to explain. We now know this pattern is unstable, and can neither have been in place for a long time (astronomically speaking) or have lasted that far into the future.

This study found that some of the swallowed galaxy remnants conform to the same pattern, but surprisingly, it is the much older set that do this, rather than the more recent arrival. This suggests these long-lost galaxies also once lay in a similar plane, indicating an abiding underlying structure to the local area of the universe. The most likely explanation is the universe is made up of a web of dark matter filaments and Andromeda lies on one of these, with gravity so powerful it aligns the movement of clusters of small galaxies.

Source www.iflscience.com

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Visiting interstellar comet is caught on camera

Image Credit: Gemini Observatory / NSF / AURA

A two-color composite image of the visiting comet. 

Astronomers have revealed that comet 2I/Borisov is remarkably similar to comets from our own solar system.

First observed on August 30th, the comet, which is the second confirmed interstellar visitor to our solar system, was announced last month by the Minor Planet Center (MPC) at Harvard University.

The first, an object known as ‘Oumuamua, was discovered back in 2017.

Perhaps the most remarkable thing about 2I/Borisov however is just how unremarkable it actually is.

“This is the first comet known to science that arrived from outside the solar system, and it is completely similar to those we see inside the solar system,” said astronomer Michal Drahus.

Its discovery suggests that there are several nearby solar systems very much like our own and that comets like those we find in our local neighborhood are not uncommon elsewhere in the universe.

Observations using the William Herschel Telescope on La Palma, Spain and the Gemini North telescope on Mauna Kea, Hawaii have shown that 2I/Borisov has a distinctive and familiar coma (a billowing cloud of gas and dust) as well as a short, fat tail.

Its nucleus is thought to be 2km wide .

“This appears to be a completely unremarkable comet on a very remarkable orbit,” said astronomer Colin Snodgrass from Edinburgh University.

“It’s very interesting that this interstellar comet looks like our own ones.”

“It implies that some of the formation processes we are trying to figure out with detailed observation of comets and asteroids, or space missions like Rosetta, are common between stars.”

Source: Guardian

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Study Reveals Six Galaxies Undergoing Sudden, Dramatic Transitions

Galaxies come in a wide variety of shapes, sizes and brightnesses, ranging from humdrum ordinary galaxies to luminous active galaxies. While an ordinary galaxy is visible mainly because of the light from its stars, an active galaxy shines brightest at its center, or nucleus, where a supermassive black hole emits a steady blast of bright light as it voraciously consumes nearby gas and dust.

Sitting somewhere on the spectrum between ordinary and active galaxies is another class, known as low-ionization nuclear emission-line region (LINER) galaxies. While LINERs are relatively common, accounting for roughly one-third of all nearby galaxies, astronomers have fiercely debated the main source of light emission from LINERs. Some argue that weakly active galactic nuclei are responsible, while others maintain that star-forming regions outside the galactic nucleus produce the most light.

A team of astronomers observed six mild-mannered LINER galaxies suddenly and surprisingly transforming into ravenous quasars–home to the brightest of all active galactic nuclei. The team reported their observations, which could help demystify the nature of both LINERs and quasars while answering some burning questions about galactic evolution, in the Astrophysical Journal on September 18, 2019. Based on their analysis, the researchers suggest they have discovered an entirely new type of black hole activity at the centers of these six LINER galaxies.

“For one of the six objects, we first thought we had observed a tidal disruption event, which happens when a star passes too close to a supermassive black hole and gets shredded,” said Sara Frederick, a graduate student in the University of Maryland Department of Astronomy and the lead author of the research paper. “But we later found it was a previously dormant black hole undergoing a transition that astronomers call a ‘changing look,’ resulting in a bright quasar. Observing six of these transitions, all in relatively quiet LINER galaxies, suggests that we’ve identified a totally new class of active galactic nucleus.”

All six of the surprising transitions were observed during the first nine months of the Zwicky Transient Facility (ZTF), an automated sky survey project based at Caltech’s Palomar Observatory near San Diego, California, which began observations in March 2018. UMD is a partner in the ZTF effort, facilitated by the Joint Space-Science Institute (JSI), a partnership between UMD and NASA’s Goddard Space Flight Center.

Changing look transitions have been documented in other galaxies–most commonly in a class of active galaxies known as Seyfert galaxies. By definition, Seyfert galaxies all have a bright, active galactic nucleus, but Type 1 and Type 2 Seyfert galaxies differ in the amount of light they emit at specific wavelengths. According to Frederick, many astronomers suspect that the difference results from the angle at which astronomers view the galaxies.

Type 1 Seyfert galaxies are thought to face Earth head-on, giving an unobstructed view of their nuclei, while Type 2 Seyfert galaxies are tilted at an oblique angle, such that their nuclei are partially obscured by a donut-shaped ring of dense, dusty gas clouds. Thus, changing look transitions between these two classes present a puzzle for astronomers, since a galaxy’s orientation towards Earth is not expected to change.

Frederick and her colleagues’ new observations may call these assumptions into question.

© R. Buta (University of Alabama/Image enhancement: Jean-Baptiste Faur Spiral Seyfert Galaxy NGC 3081: Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.

© R. Buta (University of Alabama/Image enhancement: Jean-Baptiste Faur
Spiral Seyfert Galaxy NGC 3081: Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.

“We started out trying to understand changing look transformations in Seyfert galaxies. But instead, we found a whole new class of active galactic nucleus capable of transforming a wimpy galaxy to a luminous quasar,” said Suvi Gezari, an associate professor of astronomy at UMD, a co-director of JSI and a co-author of the research paper. “Theory suggests that a quasar should take thousands of years to turn on, but these observations suggest that it can happen very quickly. It tells us that the theory is all wrong. We thought that Seyfert transformation was the major puzzle. But now we have a bigger issue to solve.”

Frederick and her colleagues want to understand how a previously quiet galaxy with a calm nucleus can suddenly transition to a bright beacon of galactic radiation. To learn more, they performed follow-up observations on the objects with the Discovery Channel Telescope, which is operated by the Lowell Observatory in partnership with UMD, Boston University, the University of Toledo and Northern Arizona University. These observations helped to clarify aspects of the transitions, including how the rapidly transforming galactic nuclei interacted with their host galaxies.

“Our findings confirm that LINERs can, in fact, host active supermassive black holes at their centers,” Frederick said. “But these six transitions were so sudden and dramatic, it tells us that there is something altogether different going on in these galaxies. We want to know how such massive amounts of gas and dust can suddenly start falling into a black hole. Because we caught these transitions in the act, it opens up a lot of opportunities to compare what the nuclei looked like before and after the transformation.”

Unlike most quasars, which light up the surrounding clouds of gas and dust far beyond the galactic nucleus, the researchers found that only the gas and dust closest to the nucleus had been turned on. Frederick, Gezari and their collaborators suspect that this activity gradually spreads from the galactic nucleus–and may provide the opportunity to map the development of a newborn quasar.

“It’s surprising that any galaxy can change its look on human time scales. These changes are taking place much more quickly than we can explain with current quasar theory,” Frederick said. “It will take some work to understand what can disrupt a galaxy’s accretion structure and cause these changes on such short order. The forces at play must be very extreme and very dramatic.”

In addition to Frederick and Gezari, UMD-affiliated co-authors of the research paper include Adjunct Associate Professor of Astronomy Bradley Cenko, former Neil Gehrels Prize Postdoctoral Fellow Erin Kara and astronomy graduate student Charlotte Ward.

More information: Sara Frederick et al, A New Class of Changing-look LINERs, The Astrophysical Journal (2019). DOI: 10.3847/1538-4357/ab3a38

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Headline Image: © (Left; infrared & visible light imagery): ESA/Hubble, NASA and S. Smartt (Queen’s University Belfast); (Right; artist’s concept): NASA/JPL-Caltech

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Giant black hole at centre of Milky Way exploded ‘recently’ – and blast was felt 200,000 light-years away

THE SUPERMASSIVE black hole at the centre of the Milky Way exploded 3.5million years ago, according to astronomers.

This is considered to be ‘astonishingly recent’ in galactic terms and is changing what scientists thought they knew about our galaxy.

This artist’s impression shows the huge bursts of radiation exploding from the centre of the Milky Way and reaching the Magellanic Stream

Professor Lisa Kewley, who worked on the study, said: “This is a dramatic event that happened a few million years ago in the Milky Way’s history.

“A massive blast of energy and radiation came right out of the galactic centre and into the surrounding material.

“This shows that the centre of the Milky Way is a much more dynamic place than we had previously thought. It is lucky we’re not residing there!”

The cataclysmic blast ripped through our galaxy and was likely felt 200,00 light years away in the Magellanic Stream.

The diameter of the Milky Way itself is thought to be up to 200,000 light years in size

It is considered to be a recent event because when it happened the dinosaurs had already been wiped out for 63million years and human ancestors were already walking on Earth.

This black hole blast phenomenon is known as a Seyfert flare.

The astronomers think it would have created two enormous ‘ionisation cones’ that would have sliced through the Milky Way.

They think it was caused by nuclear activity in the gigantic black hole, known as Sagittarius A.

It is estimated to have lasted for around 300,000 years, which is extremely short in galactic terms.

Co-author Magda Guglielmo from the University of Sydney said: “These results dramatically change our understanding of the Milky Way.

“We always thought about our Galaxy as an inactive galaxy, with a not so bright centre.

“These new results instead open the possibility of a complete reinterpretation of its evolution and nature.

“The flare event that occurred three million years ago was so powerful that it had consequences on the surrounding of our Galaxy.

“We are the witness to the awakening of the sleeping beauty.”

The research was led by by Professor Joss Bland-Hawthorn from Australia’s ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D).

During the study, data was gathered by the Hubble Space Telescope and used to calculate when and how the explosion took place.

It will soon be published in The Astrophysical Journal.

What is a black hole? The key facts

Here’s what you need to know…

What is a black hole?

  • A black hole is a region of space where absolutely nothing can escape
  • That’s because they have extremely strong gravitational effects, which means once something goes into a black hole, it can’t come back out
  • They get their name because even light can’t escape once it’s been sucked in – which is why a black hole is completely dark

What is an event horizon?

  • There has to be a point at which you’re so close to a black hole you can’t escape
  • Otherwise literally everything in the universe would have been sucked into one
  • The point at which you can no longer escape from a black hole’s gravitational pull is called the event horizon
  • The event horizon varies between different black holes, depending on their mass and size

What is a singularity?

  • The gravitational singularity is the very centre of a black hole
  • It’s a one-dimensional point that contains an incredibly large mass in an infinitely small space
  • At the singularity, space-time curves infinitely and the gravitational pull is infinitely strong
  • Conventional laws of physics stop applying at this point

How are black holes created?

  • Most black holes are made when a supergiant star dies
  • This happens when stars run out of fuel – like hydrogen – to burn, causing the star to collapse
  • When this happens, gravity pulls the centre of the star inwards quickly, and collapses into a tiny ball
  • It expands and contracts until one final collapse, causing part of the star to collapse inward thanks to gravity, and the rest of the star to explode outwards
  • The remaining central ball is extremely dense, and if it’s especially dense, you get a black hole

Source newsamed.com

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