Like a confectioner trying to reach the right consistency in a sweet concoction, a supermassive black hole is vigorously stirring the gas within a collection of galaxies to keep star formation at a minimum. The new finding, revealed bythe doomed spacecraft Hitomi, may help solve the question of why so few stars form within collections of hundreds or thousands of galaxies.

Hitomi measured the motion of gas in the center of the Hitomi measured the motion of gas in the center of the the Perseus galaxy cluster with unprecedented precision, as much as 50 times better than previous instruments, said Andrew Fabian, a professor of astronomy at the University of Cambridge in England. The black hole, by stirring the gas, keeps the material from cooling down and forming new stars. 

Without that mixing activity from the black hole, "the central galaxy would be much brighter and have a much higher stellar mass," Fabian told Space.com by email. Fabian is chairperson of part of Hitomi's science working group, an international collaboration headed by the Japan Aerospace Exploration Agency (JAXA). That group published the results of the only science completed by the HItomi spacecraft before it disintegrated in orbit last April. [Images: Black Holes of the Universe]

"We already knew that supermassive black holes, which are found at the center of all galaxy clusters and are tens of billions of times more massive than the sun, could play a major role in keeping the gas from cooling by somehow injecting energy into it," Norbert Werner, a research associate at Stanford University in California who analyzed data from Hitomi, said in a statement. "Now we understand this mechanism better and see that there is just the right amount of stirring motion to produce enough heat."

A massive spoon

Galaxy clusters are made up of anywhere from 50 to thousands of galaxies. Hot gas reaching tens of millions of degrees Fahrenheit makes up about 15 percent of a cluster, causing it to shine brightly in the X-ray spectrum. Studying the gas helps astronomers make estimates of how massive the cluster is, but these estimates can change based on how quickly the gas is stirred, a process that can also affect the birth of stars. 

Other instruments have studied the Perseus cluster, the brightest X-ray cluster in the sky, and one of the most massive. These glimpses revealed enormous bubbles of gas thousands of light-years wide, spat out by thesupermassive black hole at the center of the cluster. 

For the first time, Hitomi was able to link the movement of the gas to the bubbles. As they rise from the black hole, the bubbles drag gas from the center of the cluster, stirring it up and heating it. Because the gas can't cool, it is unable to form new stars. (Visible-light images reveal streaks of colder gas pulled away from the galactic center).

"Although the motions heat the gas at the center of the Perseus cluster, their speed is only about 100 miles [160 kilometers] per second, which is surprisingly slow considering how disturbed the region looks in X-ray images," Hitomi's co-principal investigator Roger Blandford, a physics professor at Stanford University and a professor of astrophysics and particle physics at the Department of Energy's SLAC National Accelerator Laboratory.

While understanding how the gas moves can affect estimates of mass in the cluster, Blandford said the new measurements haven't led to significant changes in previous mass calculations. 

Unfortunately, Hitomi was able to study the Perseus cluster only briefly before the satellite was lost.

Due to the spacecraft failure, "We are not able to make these measurements in other clusters and galaxies and so understand better how the feedback process operates," Fabian said.

The research, along with an accompanying perspective piece, was published online today (July 6) in the journal Nature.

'A new chapter'

Launched in February 2016, Hitomi carried an X-ray detector that was designed to spot objects 10 to 100 times fainter than those visible to previous spacecraft, according to JAXA. By probing high-energy objects such as black holes, galaxy clusters and supernova remnants from space, Hitomi was able to observe in X-ray and gamma-ray wavelengths that can't make it through Earth's atmosphere.

But after a little more than a month in space, a glitch resulted in Hitomi spinning wildly out of control. The high-speed rotation caused several pieces of the satellite to snap off, permanently disabling the spacecraft. As many as 11 fragments were detected flying through space. By the end of April, JAXA ended its efforts to reconnect to the spacecraft, well before the end of what was supposed to be a three-year mission.

Despite its early destruction, Hitomi managed to perform significant science. In its first week after launch, the spacecraft spent three days observing the Perseus cluster, making a total of four observations. Hitomi began its fateful position change before the craft had completed all of the studies that researchers had intended it to make.

"Eventually, it would have mapped much of the cluster over a total of a month or more, and much longer on many other clusters," Fabian said.

He told Space.com that only a handful of other sources were observed for calibration purposes, and these would be "much less interesting scientifically."

"Being able to measure gas motions is a major advance in understanding the dynamic behavior of galaxy clusters and its ties to cosmic evolution," study co-author Irina Zhuravleva of the Kavli Institute for Particle Astrophysics and Cosmology, said in the same statement from SLAC National Accelerator Laboratory. "Although the Hitomi mission ended tragically after a very short period of time, it's fair to say that it has opened a new chapter in X-ray astronomy."

Follow Nola Taylor Redd on Twitter @NolaTRedd or Google+. Follow us at@Spacedotcom, Facebook or Google+. Originally published on Space.com.

Paul Sutter is an astrophysicist at The Ohio State University and the chief scientist at Columbus, Ohio's Center Of Science and Industry (COSI) . Sutter is also host of the podcasts "Ask a Spaceman" and "RealSpace," and the YouTube series "Space in Your Face."

Glittering, glamorous, graceful. The latest red-carpet fashion statement? No, of course not. I'm talking about nebulas, the wispy clouds of gas and dust scattered through each galaxy. Earthly fabrics can't come close to the heavenly, tenuous beauty of these objects.

Peppered throughout the Milky Way, they provide amateur astronomers an eyeful of delight and give professional astronomers plenty to ponder. We see these objects in all sorts of shapes, sizes, colors and configurations, from almost-perfect spheres and shells to dazzlingly complex helices to tangled wrecks. But where exactly do they come from? And, perhaps more importantly, where are they going?

[Watch this video where I describe Messier's catalog of nebulas.]

Into the stars

To get a good look at nebulas, let's first look at the stars. Tiny, compact and dense — at least, astronomically speaking — a star is pretty much the opposite of a nebula. The power of a star comes from nuclear fusion, which occurs because of the intense pressures shoving elements together way past their personal comfort zones. That fusion creates heavier elements and a tiny bit of leftover energy, which is enough to maintain the star for millions (in the case of huge stars) to trillions (in the case of teensy-tiny-barely-above-brown-dwarf stars) of years. [50 Fabulous Deep-Space Nebula Photos]

No matter how long they last, stars are finite creatures. Thus, they must have come from somewhere and will end up going to somewhere else. Presumably, they didn't start life as tiny, dense balls and they won't end life the same way either. So where do stars come from, and where are they going?

Based on this article's topic, you can probably guess what the answer is: nebulas. Stars come from nebulas and end up turning into nebulas. Likewise, nebulas can generally be classified into two categories: about-to-be-stars and used-to-be-stars.

About to be stars

One could argue that the natural state of matter is clouds of stuff. In fact, I'm about to make just that argument. Stars depend on a specific process, nuclear fusion, to survive, and once that process ends, they quit being stars. The objects known as stars are altogether temporary. But a cloud of gas and dust? It can just hang out being a cloud of gas and dust for as long as it wants. If no forces nudge it one way or the other, it's perfectly happy just being what it is.

That will change only when a nebula does get nudged, say by a chance gravitational interaction with a neighbor, or by being too close to a nearby supernova (you gotta hate it when that happens). Once nudged, the nebula can become unstable, its natural self-gravitational pull overwhelming its equally natural gas pressure (an event marked by reaching a threshold dubbed the "Jeans instability"). Very quickly, pieces of the nebula branch and break off, smashing down in on themselves to get the fusion party started and make some stars.

The smashed-down bits turn into "dark nebulas" (hint: they're kind of black) as their high densities shroud the light coming from any newly forming stars. Fortunately, radio and infrared radiation penetrate even the densest of these nebulas, allowing astronomers to peer into these clouds' stellar wombs.

A typical cloud of gas, once unsettled, might make hundreds or even thousands of stars in a single batch. The largest and brightest of those stars will spew out tons of hot, heavy, high-energy radiation, exciting the molecules in the remaining nebula and causing it to glow rosy red.

Called "emission nebulas" — because their material is, well, emitting light — they won't last long. Those big, bright stars spewing radiation are sure to go supernova, ripping apart the already-tenuous veils of dust and gas and spreading this material so thin even the keenest observers are unable to distinguish it from the general spacey background.

Used to be stars

And that brings us to where nebulas come from in the first place. The answer, of course, is stars. When stars die, it's not pretty — or it's very pretty, depending on your point of view. [Supernova Photos: Great Images of Star Explosions]

The largest stars go off in spectacular fashion, unleashing almost all their unspent energy in a blast that can outshine entire galaxies (to be fair, the blast will last only a few days or weeks, while galaxies keep on shining for trillions of years). That blast naturally carries a lot of "stuff" far from the original star; basically, the whole star is turned inside out and goes from point-like to cloud-like in one fantastic event.

The ejected material rides the shockwaves at a healthy fraction of the speed of light, so it doesn't take long for a decent-size nebula to form. Even supernovas that occurred only hundreds of years ago (which in astronomical terms might as well be yesterday) have already become beautiful artistic displays. One such example is the Crab nebula, which is itself lit by the intense radiation still pouring out of the hot, left-over core of its dead star.

Stars like Earth's sun don't go off as intensely, but that doesn't mean they don't get to create their own masterpieces. Near the ends of these stars' lives, the switchover from hydrogen- to helium-based fusion in the cores leads to complex interplay in the stellar interiors. This causes the outmost layers to swell, expand and eventually slough off. The erratic nature of the star during this time pushes the outward-moving gas in weird directions.

The result: planetary nebulas, which unfortunately have absolutely nothing to do with planets. They come in a wild variety of shapes and patterns. They don't last long. Like their supernova cousins, they're lit by the remaining core of the star, and once that peters out after a few thousand years, the fireworks show is over.

But since stars like the Earth's sun are so common, this galaxy continues to produce new planetary nebulas, decorating the galactic disk like Christmas ornaments.

[Watch this video where I explain the life cycles of stars.]

The circle of stellar life

So that's it: Nebulas turn into stars, and stars turn into nebulas. It's a cycle that has persisted for over 13 billion years, starting when the first nebula scrunched down into a star. And it will continue to last for trillions more. Eventually, though, the nebulas will win: You need to pack enough stuff into a small enough space to make a star, and once you run out of opportunities you run out of stars, and the universe will return to its natural, long-term state: a bunch of gas and dust floating around.

Learn more by listening to the episode "Where Do Nebulae Come From?" on the "Ask a Spaceman" podcast, available on iTunes and on the Web at http://www.askaspaceman.com. Thanks to @bcmiller151 for the question that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and onfacebook.com/PaulMattSutter.

Follow all of the Expert Voices issues and debates — and become part of the discussion — on Facebook, Twitter and Google+. The views expressed are those of the author and do not necessarily reflect the views of the publisher. This article was originally published on Space.com.

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Mosaics depicting prominent Bible scenes were uncovered during annual excavations of an ancient synagogue in Israel's Lower Galilee.

During the excavation in June, archaeologists found two new panels of amosaic floor in a Late Roman (fifth-century) synagogue at Huqoq, an ancient Jewish village. One panel showed Noah's ark with pairs of animals, such as lions, leopards and bears. The other panel depicted soldiers being swallowed by large fish, surrounded by overturned chariots in the parting of the Red Sea.

Such images are extremely rare for the time period, according to excavation director Jodi Magness, of the University of North Carolina at Chapel Hill, whose work was funded by the National Geographic Society. [Photos: Unusual Mosaics Decorated Ancient Synagogue in Israel]

"I know of only two other scenes of the parting of the Red Sea in ancient synagogues," Magness told National Geographic.

"One is in the wall paintings at Dura Europos [in Syria], which is a complete scene but different from ours — no fish devouring the Egyptian soldiers," Magness said. "The other is at Wadi Hamam [in Israel], but that's very fragmentary and poorly preserved."

The ark scenes are also uncommon; Magness said she knows of only two other mosaics showing such depictions.

Along with a team of university scholars and students, and the Israel Antiquities Authority, Magness has excavated at Huqoq since 2012. Previous mosaic discoveries have depicted Bible scenes such as Samson and the foxes and Samson carrying the gate of Gaza on his shoulders.

The Huqoq excavations revealed the first nonbiblical mosaic found in an ancient synagogue. That three-tiered mosaic included a scene showing a meeting between two important male figures, thought to be the legendary meeting between Alexander the Great and the Jewish high priest.

These previous discoveries were uncovered in the synagogue's eastern aisle, and the researchers were uncertain whether the mosaics would continue into the nave, the large central area of the synagogue. However, the excavations did, indeed, reveal the Red Sea and Noah's ark mosaics.

"This panel is exactly as it should be," Magness said of the ark mosaic. "It's facing north, so people could see it as they entered from the south," where the main door would have been located.

Excavations at this site also uncovered coins spanning 2,300 years.

"The ancient coins … are critical for our knowledge of the monumental synagogue and the associated village," Nathan Elkins, a member of the research team and a professor of art history at Baylor University, said in a statement.

As is the case after each excavation season, the researchers will remove the uncovered mosaics for conservation and backfill the excavated areas. Excavations are scheduled to continue in the summer of 2017. 

Original article on Live Science.

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