tidal disruptions


Black Hole Caught Devouring Star For An Entire Decade

“Normally lasting weeks or months, a new record has just been set for TDEs. XJ1500+0154, 1.8 billion light years away, is the largest, longest-lasting one ever seen. First detected in July of 2005, the X-rays from this distant source brightened by a factor of 100 over 3 years. They remain bright even today. Although dozens of TDEs have been observed since the 1990s, none have lasted this long. It may be caused by the most massive star ever observed creating a TDE.”

When any object passes too close to the event horizon of a black hole, the tidal forces acting on it can become so strong that they’ll tear the entire object apart in a spaghettification disaster. While most of the matter will get ejected from the encounter, a significant fraction can be accreted, absorbed and used to fuel the black hole’s growth. These tidal disruption events have been seen numerous times since the launch of our X-ray observatories, and are now known to come in a wide variety of magnitudes, at a variety of distances and to last a variable amount of time. So when you see the largest, longest-lasting one ever, you sit up and take notice! That’s exactly what’s happened with XJ1500+154, which is now in its second decade of X-ray signals.

Come get the full story on this amazing object, and learn how it might solve the puzzle of supermassive black hole growth on today’s Mostly Mute Monday!

The Sunflower Galaxy, Messier 63 sports a bright yellowish core in this sharp composite image from space- and ground-based telescopes. Its sweeping blue spiral arms are streaked with cosmic dust lanes and dotted with pink star forming regions. A bright spiral galaxy of the northern sky, M63 is about 25 million light-years distant in the loyal constellation Canes Venatici. A dominant member of a known galaxy group, M63 has faint, extended features that are likely star streams from tidally disrupted satellite galaxies. M63 shines across the electromagnetic spectrum and is thought to have undergone bursts of intense star formation. 

Image Credit & Copyright: Data - Hubble Legacy Archive, Subaru Telescope (NAOJ), Don Goldman Processing - Robert Gendler, Roberto Colombari, Don Goldman

Messier 63: The Sunflower Galaxy 

 A bright spiral galaxy of the northern sky, Messier 63 is about 25 million light-years distant in the loyal constellation Canes Venatici. Also cataloged as NGC 5055, the majestic island universe is nearly 100,000 light-years across. That’s about the size of our own Milky Way Galaxy.

Known by the popular moniker, The Sunflower Galaxy, M63 sports a bright yellowish core in this sharp composite image from space- and ground-based telescopes. Its sweeping blue spiral arms are streaked with cosmic dust lanes and dotted with pink star forming regions. A dominant member of a known galaxy group, M63 has faint, extended features that are likely star streams from tidally disrupted satellite galaxies. M63 shines across the electromagnetic spectrum and is thought to have undergone bursts of intense star formation. 

Credit: Data - Hubble Legacy Archive, Subaru Telescope (NAOJ), Don Goldman, Processing - Robert Gendler, Roberto Colombari, Don Goldman

Dueling Whirlpools – Rule Calls on the Fly

So, a few weeks ago, Steve, who plays Eustace the Minotaur Cleric in my 5E game, discovered just how effective the Control Water spell is in a naval battle. He cast it when the group was attacked by some aquatic trolls and their pet giant shark. Suddenly, a tricky battle with undersea foes turned into something very different, with the shark needing to flop back into the water and the trolls fully exposed.

This made me step back and do a lot of thinking about other encounters coming up. One was with a group of raiders (with stats and even names directly lifted from the Princes of the Apocalypse) who would be attacking the group by ship. I would never want to penalize a player for coming up with an intelligent use of a spell, but I also wanted to demonstrate that they needed to be wary of relying on the same tactic for every fight. An intelligent foe would take steps to counter what they were doing. Therefore, I made sure that Gar Shatterkeel, the raiders’ leader, would have Control Water as well.

As I’d guessed, Steve was quick to cast Control Water…and so was Gar. I had him made a Wisdom check to reflect his realization that someone else was countering what he was doing. He smiled. “Oh? Well, I guess we’ll see who’s god is stronger.”

So I suddenly needed a mechanic to reflect this duel of wills. Since it was based on will, Wisdom made sense as the stat to use. Every time one of them tried to influence the water, I had the two of them make opposed Wisdom checks. Whoever succeeded had control, and, depending on how much they’d succeeded by, I let them more powerfully stay in control and influence things. It made for an exciting fight in three dimensions. Water got lowered and raised, ships got caught in whirlpools. At one point, another caster on the enemy side hit the party’s ship with a Tidal Wave spell, which disrupted Eustace’s spell long enough for Gar to get his ships repositioned after a whirlpool, but he was able to get a second spell up and running before Gar could do much damage to them.

In the end, as the night ran long, and it was clear the raiders were losing, I had Gar pull back. Although the party couldn’t stop his flagship from departing, they were able to stop a couple of smaller ships. At one point, I let the party’s Warlock use Flaming Sphere to hull a ship. Eustace also wanted to use Stone Shape to turn part of their dwarven stoneship’s hull into a spike to jut out and put a hole in a damaged ship’s frame, speeding along its sinking. I allowed it. Is that how those spells are normally used? Nope. Do I care? I do not. I had already assumed those ships were going to be destroyed, and the night was getting late. Letting things proceed this way just sped it along, and those players got to feel really cool.

Here’s an important secret – the most important thing about the game is making it fun. If you bend and even break rules to make it more fun for everyone, there are no D&D police that’re going to show up at your house and tell you you’re doing it wrong. When you’re running a game in a public venue, it’s best to try and try to the rules as they’re written, but your home game is YOURS. I’ve let PCs flip over opponents and make a strike mid-leap to gain Advantage. I’ve let them use spells in ways they weren’t written to do. I’ve let them befriend elementals and monsters if it made things interesting.

I challenge any GM reading my material to embrace the improve rules of “Yes, And…” and “Yes, But…” Don’t shut things down. Let crazy plans succeed. Let spells work differently. Make the players make Arcana rolls to “power stunt” the spell, if you wish, but let them have that moment. It’ll make for stories they’ll remember and retell, and, in the end, that might be the best reward of playing RPGs.


What’s The Largest Galaxy In The Universe?

“Interacting spiral galaxies can have their arms greatly extended and disrupted, with NGC 6872 spanning 522,000 light years from tip-to-tip. Ultra-low surface brightness galaxies can see their stars extend even farther, with Malin 1 reaching 650,000 light years across. […]  But the largest and most massive galaxies aren’t spirals, but supergiant ellipticals, like NGC 4874 in the Coma Cluster.”

From our vantage point within the Milky Way, it sure does appear impressive. Hundreds of billions of stars shine in our own cosmic backyard, with our galaxy spanning a whopping 100,000 light years from end-to-end. Yet not only is that small compared to our nearest large neighbor, Andromeda, but it’s not even 20% as large as the largest spiral galaxies we find. While tidal disruption might create the largest spiral galaxies, we have giant ellipticals that are many times larger than a spiral will ever achieve. Some of the biggest ones of all are found at the centers of massive galaxy clusters, but in the scheme of the entire observable Universe, only one galaxy can truly be the largest.

Which is it, and how do we know? Find out on this edition of Mostly Mute Monday!

This awesome illustration shows a glowing stream of material from a star, being left behind as it was being devoured by a supermassive black hole! The black hole is surrounded by a ring of dust. 

When a star passes a black hole and is close enough to be swallowed, stellar material gets stretched and compressed as it is pulled in. A black hole’s destruction of a star, called “stellar tidal disruption,” releases an enormous amount of energy, brightening the surroundings in an event called a flare. 

In recent years, a few dozen such flares have been discovered, but they are not well understood.

Image credit: NASA/JPL-Caltech

Black (Hole) Friday!

It’s Black Friday, but for us, it’s the annual Black Hole Friday! Today, we’ll post awesome images and information about black holes.

A black hole is a place in space where gravity pulls so much that even light cannot get out. The gravity is so strong because matter has been squeezed into a tiny space…sort of like all of those shoppers trying to fit into the department stores today.

Because no light can get out, you can’t see black holes with the naked eye. Space telescopes with special tools help find black holes (similar to how those websites help you discover shopping deals).

How big are black holes? Black holes can be large or small…just like the lines in all of the stores today. Scientists think the smallest black holes are as small as just one atom. These black holes are very tiny but have the mass of a large mountain! 

So how do black holes form? Scientists think the smallest black holes formed when the universe began. Stellar black holes are made when the center of a very big star collapses. When this happens, it causes a supernova

A supernova is an exploding star that blasts part of its mass into space. 

Supermassive black holes are an altogether different story. Scientists think they were made at the same time as the galaxy they in they reside. Supermassive black holes, with their immense gravitational pull, are notoriously good at clearing out their immediate surroundings by eating nearby objects. 

When a star passes within a certain distance of a black hole, the stellar material gets stretched and compressed – or “spaghettified” – as the black hole swallows it. A black hole destroying a star, an event astronomers call “stellar tidal disruption,” releases an enormous amount of energy, brightening the surroundings in an event called a flare. In recent years, a few dozen such flares have been discovered.

Then there are ultramassive black holes, which are found in galaxies at the centers of massive galaxy clusters containing huge amounts of hot gas.

Get more fun facts and information about black holes.

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Spinning black hole swallows star; surpasses all supernovae in brightness

“Almost every galaxy, even quiet, red ones, contain supermassive black holes at their core. When matter approaches – whether an asteroid, planet, gas cloud or a star – the incredible tidal forces stretch and pinch it, tearing it apart into a long, thin strand. Some of these black holes can rotate incredibly rapidly, causing the matter that falls in to accelerate at different rates depending on the orientation and configuration of the infall, which changes over time. The ASASSN-15lh event not only showed an ultraviolet re-brightening, but a rapid temperature spike at late times as well. If the explanation pans out, this would be the first time we’ve ever observed a rare event of this kind: a massive star disrupted and devoured by an ultramassive, rapidly spinning supermassive black hole.”

Last year, a record-shattering event occurred: we saw the brightest supernova ever observed in the Universe. It outshone the previous record holder by more than double, and it reached a peak brightness of more than 20 times the sum total of all the stars in the Milky Way galaxy. Surprisingly, it occurred in a red, quiet galaxy, rather than the bright blue ones famous for them. After 10 months of follow-up observations, it looks like it wasn’t a supernova after all. Instead of fading away, there was a rebrightening months after the peak. Instead of cooling down, something reheated the glow to even greater temperatures. The only thing that fits the data? A tidal disruption event, and even those would only work if it were a supermassive black hole that rotated more quickly than any such event ever observed before.

Come get the full spectacular story – and the science behind it – as we finally learn where the brightest event in history came from!

(NASA)  Arp 188 and the Tadpole’s Tail
Image Credit: Hubble Legacy Archive, ESA, NASA; Processing & Copyright: Joachim Dietrich

Why does this galaxy have such a long tail? In this stunning vista, based on image data from the Hubble Legacy Archive, distant galaxies form a dramatic backdrop for disrupted spiral galaxy Arp 188, the Tadpole Galaxy. The cosmic tadpole is a mere 420 million light-years distant toward the northern constellation Draco. Its eye-catching tail is about 280 thousand light-years long and features massive, bright blue star clusters. One story goes that a more compact intruder galaxy crossed in front of Arp 188 - from right to left in this view - and was slung around behind the Tadpole by their gravitational attraction. During the close encounter, tidal forces drew out the spiral galaxy’s stars, gas, and dust forming the spectacular tail. The intruder galaxy itself, estimated to lie about 300 thousand light-years behind the Tadpole, can be seen through foreground spiral arms at the upper right. Following its terrestrial namesake, the Tadpole Galaxy will likely lose its tail as it grows older, the tail’s star clusters forming smaller satellites of the large spiral galaxy.


Cosmic ‘Spitballs’ Released From Milky Way’s Black Hole

“Black holes don’t just provide gravity, absorb incoming matter and prevent anything from escaping. They also gravitationally pull on and tear matter that passes nearby, including stars. In a surprising find, a new study out of Harvard shows that torn-apart stars aren’t merely reduced into gas, but they form dense streams that re-condense into planets in just year-long timescales. Moving rapidly away from the central black hole, these 'cosmic spitballs’ represent a brand new population of rogue planets, and are potentially the most catastrophic objects from space careening through our galaxy.”

Imagine you’re a star passing too close to a black hole. What’s going to happen to you? Yes, you’ll be tidally disrupted and eventually torn apart. Some of the matter will be swallowed, some will wind up in an accretion disk, and some will be accelerated and ejected entirely. But quite surprisingly, the ejected matter doesn’t just come out in the form of hot gas, but it condenses into large numbers of rapidly-moving planets. This population should make up approximately one out of every 1000 rogue planets, but should be uniquely identifiable. The vast majority will move at incredible speeds of around 10,000 km/s, be approximately the mass of Jupiter but will be made out of shredded star material, rather than traditional planetary material. As the next generation of infrared telescopes come online, these ‘cosmic spitballs’ should be one of the most exciting novel discoveries of all.

Come get the whole story on cosmic spitballs, fresh from the AAS meeting!


Mostly Mute Monday: Crater Chains of the Moon

“While craters young and old litter its surface, large numbers of catenae, or crater chains, can be found as well on both the near and far sides. While about 20 have been known since the 1990s, often extending for hundreds of kilometers, many more have been discovered with the advent of LROC and citizen science projects like Moon Zoo.”

You might think that your odds of getting 3, 5, or even 10 or more craters all next to each other and in a row on an object like the Moon are astronomically small. Yet, we’ve identified dozens of features that show exactly this! Here are some of the most spectacular, along with the redux of the leading ideas of where they came from, including secondary impacts, tidally disrupted impactors and volcanic and geologic explanations.



– The discovery of two massive holes punched through a stream of stars could help answer questions about the nature of dark matter, the mysterious substance holding galaxies together.–

Researchers have detected two massive holes which have been ‘punched’ through a stream of stars just outside the Milky Way, and found that they were likely caused by clumps of dark matter, the invisible substance which holds galaxies together and makes up a quarter of all matter and energy in the universe.

The scientists, from the University of Cambridge, found the holes by studying the distribution of stars in the Milky Way. While the clumps of dark matter that likely made the holes are gigantic in comparison to our Solar System – with a mass between one million and 100 million times that of the Sun – they are actually the tiniest clumps of dark matter detected to date.

The results, which have been submitted to the Monthly Notices of the Royal Astronomical Society, could help researchers understand the properties of dark matter, by inferring what type of particle this mysterious substance could be made of. According to their calculations and simulations, dark matter is likely made up of particles more massive and more sluggish than previously thought, although such a particle has yet to be discovered.

“While we do not yet understand what dark matter is formed of, we know that it is everywhere,” said Dr Denis Erkal from Cambridge’s Institute of Astronomy, the paper’s lead author. “It permeates the universe and acts as scaffolding around which astrophysical objects made of ordinary matter – such as galaxies – are assembled.”

Current theory on how the universe was formed predicts that many of these dark matter building blocks have been left unused, and there are possibly tens of thousands of small clumps of dark matter swarming in and around the Milky Way. These small clumps, known as dark matter sub-haloes, are completely dark, and don’t contain any stars, gas or dust.

Dark matter cannot be directly measured, and so its existence is usually inferred by the gravitational pull it exerts on other objects, such as by observing the movement of stars in a galaxy. But since sub-haloes don’t contain any ordinary matter, researchers need to develop alternative techniques in order to observe them.

The technique the Cambridge researchers developed was to essentially look for giant holes punched through a stream of stars. These streams are the remnants of small satellites, either dwarf galaxies or globular clusters, which were once in orbit around our own galaxy, but the strong tidal forces of the Milky Way have torn them apart. The remnants of these former satellites are often stretched out into long and narrow tails of stars, known as stellar streams.

“Stellar streams are actually simple and fragile structures,” said co-author Dr Sergey Koposov. “The stars in a stellar stream closely follow one another since their orbits all started from the same place. But they don’t actually feel each other’s presence, and so the apparent coherence of the stream can be fractured if a massive body passes nearby. If a dark matter sub-halo passes through a stellar stream, the result will be a gap in the stream which is proportional to the mass of the body that created it.”

The researchers used data from the stellar streams in the Palomar 5 globular cluster to look for evidence of a sub-halo fly-by. Using a new modelling technique, they were able to observe the stream with greater precision than ever before. What they found was a pair of wrinkled tidal tails, with two gaps of different widths.

By running thousands of computer simulations, the researchers determined that the gaps were consistent with a fly-by of a dark matter sub-halo. If confirmed, these would be the smallest dark matter clumps detected to date.

“If dark matter can exist in clumps smaller than the smallest dwarf galaxy, then it also tells us something about the nature of the particles which dark matter is made of – namely that it must be made of very massive particles,” said co-author Dr Vasily Belokurov. “This would be a breakthrough in our understanding of dark matter.”

The reason that researchers can make this connection is that the mass of the smallest clump of dark matter is closely linked to the mass of the yet unknown particle that dark matter is composed of. More precisely, the smaller the clumps of dark matter, the higher the mass of the particle.

Since we do not yet know what dark matter is made of, the simplest way to characterise the particles is to assign them a particular energy or mass. If the particles are very light, then they can move and disperse into very large clumps. But if the particles are very massive, then they can’t move very fast, causing them to condense – in the first instance – into very small clumps.

“Mass is related to how fast these particles can move, and how fast they can move tells you about their size,” said Belokurov. “So that’s why it’s so interesting to detect very small clumps of dark matter, because it tells you that the dark matter particle itself must be very massive.”

“If our technique works as predicted, in the near future we will be able to use it to discover even smaller clumps of dark matter,” said Erkal. “It’s like putting dark matter goggles on and seeing thousands of dark clumps each more massive than a million suns whizzing around.”

TOP IMAGE….artist’s impression of dark matter clumps around a Milky Way-like galaxy. These clumps are invisible and can only be detected through their gravitational effect on visible matter. The clumps, also known as subhaloes, come in a range of sizes with the smallest one set by the mass of the yet to be discovered dark matter particle. The more massive the dark matter particle, the slower the dark matter moves, and the easier it is for regions in the early universe to collapse and form small subhaloes. In this work, a tidal stream from a disrupting globular cluster is used to probe their presence. Credit: V. Belokurov, D. Erkal, S.E. Koposov (IoA, Cambridge). Photo: Color image of M31 from Adam Evans. Dark matter clumps from Aquarius, Volker Springel (HITS)

LOWER IMAGE….Comparison between the observed stream and two simulated streams. The blue points show the observed stream which has been colored blue to distinguish it from the other streams. In reality, the color of its stars look more like the previous figure. Note the underdense regions on the left and right. The green points show a simulated stream evolved in a smooth potential without dark matter clumps. In contrast to the observed stream, this stream appears smooth and does not have any gaps. The red points show a simulated stream which has been struck by two clumps of dark matter with masses of one million Suns (left) and fifty million Suns (right). These perturbations produce the same gaps as what is seen in the data. Although the dark matter clumps themsevlves are invisible, they create gaps in the stream which can be detected. If confirmed, these two dark subhaloes would represent the lowest mass clumps detected to date. Credit: V. Belokurov, D. Erkal, S.E. Koposov (IoA, Cambridge)


Most massive collection of giant stars ever revealed by Hubble

“The single greatest is R136a1: 250 times our Sun’s mass. Nine total stars over 100 solar masses, as well as dozens over 50, are found inside. These nine largest stars, combined, outshine the Sun by 30,000,000 times. All will die in catastrophic supernovae, creating massive black holes when they do.”

When we look for the brightest, bluest, most massive individual stars, we’re restricted to looking nearby, since it’s impossible to resolve individual stars at distances that extend much beyond our own galaxy. So how surprising is it, then, when the most massive stars we’ve ever found aren’t in our own galaxy, nor in any of the monster galaxies we’ve found nearby, but in a small, satellite dwarf of our own: the Large Magellanic Cloud? The tidal disruption of the Milky Way causes a huge spike in star formation among the neutral gas, and has led to an incredibly rich region of new stars, including dozens of stars over 50 solar masses, nine over 100, four over 150 and the most massive one, R136a1, coming in at an incredible 250 times the mass of our Sun. It’s the most massive collection of hot, young stars in the entire known Universe.