Our Sun Came Late to the Milky Way's Star-Birth Party
Our Sun missed the stellar "baby boom" that erupted in our young Milky Way galaxy 10 billion years ago. During that time the Milky Way was churning out stars 30 times faster than it does today. Our galaxy was ablaze with a firestorm of star birth as its rich reservoir of hydrogen gas compressed under gravity, creating myriad stars. But our Sun was not one of them. It was a late "boomer," arising 5 billion years later, when star birth had plunged to a trickle.
Astronomers compiled this story of our Milky Way's growth from studying galaxies similar in mass to our galaxy, found in deep surveys of the universe. Stretching back in time more than 10 billion years, the census contains nearly 2,000 snapshots of Milky Way-like galaxies. The analysis comprises the most comprehensive multi-observatory galaxy survey yet, and includes data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), taken with NASA's Hubble Space Telescope.
Globular star clusters are isolated star cities, home to hundreds of thousands of stars. And like the fast pace of cities, there's plenty of action in these stellar metropolises. The stars are in constant motion, orbiting around the cluster's center. Past observations have shown that the heavyweight stars live in the crowded downtown, or core, and lightweight stars reside in the less populated suburbs.
But as heavyweight stars age, they rapidly lose mass, cool down, and shut off their nuclear furnaces. After the purge, only the stars' bright, super-hot cores remain, and they are called white dwarfs. This weight-loss program causes the now lighter-weight white dwarfs to be nudged out of the downtown through gravitational interactions with the heftier stars. At each encounter, the white dwarfs' orbits begin to expand outward from the cluster's packed center. Until these Hubble observations, astronomers had never seen the dynamical conveyor belt in action. The new Hubble results reveal young white dwarfs on their slow-paced 40-million-year exodus from the bustling center of the globular cluster 47 Tucanae in our Milky Way galaxy.
Hubble Observes One-of-a-Kind Star Nicknamed 'Nasty'
Astronomers have spent decades trying to determine the oddball behavior of an aging star nicknamed "Nasty 1" residing in our Milky Way galaxy. Nasty 1 was identified as a Wolf-Rayet star, a rapidly evolving star that is much more massive than our sun. The star loses its hydrogen-filled outer layers quickly, exposing its super-hot and extremely bright helium-burning core.
But Nasty 1 doesn't look like a typical Wolf-Rayet star. Astronomers using NASA's Hubble Space Telescope had expected to see a bipolar outflow of twin lobes of gas from the star, perhaps similar to those emanating from the massive star Eta Carinae. The astronomers were surprised, however, to find a pancake-shaped disk of gas encircling the star. The vast disk is nearly 1,000 times the diameter of our solar system. It may have formed from the interaction between Nasty 1 and an unseen companion star. The star may represent a brief transitory stage in the evolution of extremely massive stars. Nasty 1's nickname was derived from its catalog name of NaSt1.
Two of the most reliable changes in the sky are the daily rising of the sun in the east and setting of the sun in the west. But if you lived on a couple of Pluto's moons you wouldn't know when the day would begin, or even what direction the sun would rise. That's because, unlike Earth's moon, at least two of Pluto's small moons, Hydra and Nix, are tumbling chaotically through space. Why? Because they orbit inside a dynamically shifting gravitational field caused by the system's two central bodies, Pluto and Charon, that are whirling around each other. The moons are also football shaped, and this contributes to the chaotic rotation.
By contrast, Earth's moon keeps the same face toward us, because the gravitational forces between Earth and the moon cause the moon to dynamically settle into a condition called tidal lock, where it keeps one hemisphere facing Earth. Almost all of the solar system's major moons also behave similarly. But the Pluto moons essentially orbit a "double planet." And this makes life complicated. Over the past several years, the Hubble Space Telescope has discovered four tiny satellites orbiting Pluto and Charon. Researchers were puzzled by unpredictable changes in the sunlight reflected off the two brighter moons. They finally concluded that at least two of the moons must be tumbling unpredictably.
This magnificent spiral galaxy is at the edge of what astronomers call the Local Void. The Local Void is a huge volume of space that is at least 150 million light-years across that doesn't seen to contain anything much. There are no obvious galaxies. This void is simply part of the structure of the universe where matter grows clumpy over time so that galaxies form clusters and chains, which are separated by regions mostly devoid of galaxies. This results in sort of a "soap bubble" structure on large scales. The galaxy, as photographed by NASA's Hubble Space Telescope, is especially colorful where bright red patches of gas can be seen scattered through its spiral arms. Bright blue regions contain newly forming stars. Dark brown dust lanes snake across the galaxy's bright arms and center, giving it a mottled appearance.
Quasars are the light fantastic. They are the brightest beacons in the universe, blazing across space with the intrinsic brightness of one trillion suns. Yet the objects are not vast galaxies, but they appear as pinpoint sources in the biggest telescopes of today – hence the term "quasar" for quasi-stellar object. Discovered in the 1960s, it took more than two decades of research to come to the conclusion that quasars are produced by the gusher of energy coming from over-fed supermassive black holes inside the cores of very distant galaxies. And, most quasars bloomed into a brief existence 12 billion years ago.
The big question has been, why? What was happening in the universe 12 billion years ago? The universe was smaller and so crowded that galaxies collided with each other much more frequently than today. Astronomers using Hubble's near-infrared vision tested this hypothesis by looking at dusty quasars where their glow was suppressed by dust, allowing a view of the quasar's surroundings. Hubble's sharp vision revealed chaotic collisions between galaxies that gave birth to quasars by fueling a supermassive central black hole.
Join astronomers during the live Hubble Hangout discussion at 3:00 pm EDT on Thurs., June 18, to learn even more about quasars and the Hubble Space Telescope. To join, visit The "Teenage Years" of Quasars .
Hubble Finds That the Nearest Quasar Is Powered by a Double Black Hole
Quasars are the light fantastic. These brilliant cores of active galaxies blaze with the radiance of a hundred billion stars compressed into a region of space not much larger than our solar system. Supermassive black holes, with millions or billions of times the mass of our sun, are the only imaginable powerhouse behind these tsunamis of raw energy.
Hubble Space Telescope astronomers set their sights on the nearest quasar to Earth, Markarian 231, located 581 million light-years away. Black holes – even supermassive ones – are too compact to be resolved by any present-day telescope. So, astronomers did the next best thing, measure all the light from a disk of infalling material around the black hole. The ultraviolet radiation – only measurable by Hubble – revealed evidence for a curious gap in the disk. Instead of being pancake shaped, it looks more like it has a big donut hole. The best explanation for the gap is that two black holes are orbiting each other in a dizzying dance that powers the quasar fireworks. This carves out the gap. The second black hole must have come from a smaller galaxy that merged with Markarian 231 to ignite the quasar about 1 million years ago.
Mysterious Ripples Found Racing Through Planet-Forming Disk
Though astronomers have discovered thousands of planets orbiting other stars, very little is known about how they are born. The conventional wisdom is that planets coagulate inside a vast disk of gas and dust encircling newborn stars. But the details of the process are not well understood because it takes millions of years to happen as the disk undergoes numerous changes until it finally dissipates.
The young, nearby star AU Microscopii (AU Mic) is an ideal candidate to get a snapshot of planet birthing because the disk is tilted nearly edge on to our view from Earth. This very oblique perspective offers an opportunity to see structure in the disk that otherwise might go unnoticed. Astronomers are surprised to uncover fast-moving, wave-like features embedded in the disk that are unlike anything ever observed, or even predicted. Whatever they are, these ripples are moving at 22,000 miles per hour – fast enough to escape the star's gravitational pull. This parade of blob-like features stretches farther from the star than Pluto is from our sun. They are so mysterious it's not known if they are somehow associated with planet formation, or some unimagined, bizarre activity inside the disk.
The old adage "what goes up must come down" even applies to an immense cloud of hydrogen gas outside our Milky Way galaxy. First discovered in the 1960s, the comet-shaped cloud is 11,000 light-years long and 2,500 light-years across. If the cloud could be seen in visible light, it would span the sky with an apparent diameter 30 times greater than the size of the full moon. The cloud, which is invisible at optical wavelengths, is plummeting toward our galaxy at nearly 700,000 miles per hour. Hubble was used to measure the chemical composition of the cloud as a means of assessing where it came from. Hubble astronomers were surprised to find that the cloud, which is largely composed of hydrogen, also has heavier elements that could only come from stars. This means the cloud came from the star-rich disk of our galaxy. The Smith Cloud is following a ballistic trajectory and will plow back into the Milky Way's disk in about 30 million years. When it does, astronomers believe it will ignite a spectacular burst of star formation, perhaps providing enough gas to make 2 million suns.
NASA's Hubble Space Telescope is an amazing time machine; by looking back through space, astronomers actually look back through time. Now, by pushing Hubble to its limits, an international team of astronomers has shattered the cosmic distance record by viewing the farthest galaxy ever seen. Named GN-z11, this surprisingly bright, infant galaxy is seen as it was 13.4 billion years in the past. The astronomers saw it as it existed just 400 million years after the big bang, when the universe was only three percent of its current age. At a spectroscopically confirmed redshift of 11.1, the galaxy is even farther away than originally thought. It existed only 200 million to 300 million years after the time when scientists believe the very first stars started to form. At a billion solar masses, it is producing stars surprisingly quickly for such an early time. This new record will most likely stand until the launch of Hubble's successor, the James Webb Space Telescope, which will look even deeper into the universe for early galaxies.
Hubble's infrared vision pierced the dusty heart of our Milky Way galaxy to reveal more than half a million stars at its core. Except for a few blue, foreground stars, the stars are part of the Milky Way's nuclear star cluster, the most massive and densest stellar cluster in our galaxy. Located 27,000 light-years away, this region is so packed with stars, it is equivalent to having a million suns crammed into the volume of space between us and our closest stellar neighbor, Alpha Centauri, 4.3 light-years away. At the very hub of our galaxy, this star cluster surrounds the Milky Way's central supermassive black hole, which is about 4 million times the mass of our sun.
To learn even more about the Milky Way's nuclear star cluster and Hubble, join astronomers and scientists during a live Hubble Hangout discussion at 3pm EDT on Thurs., March 31 at Heart of the Milky Way Galaxy.
Imagine driving through a small town containing modest-sized buildings and seeing a 100-story skyscraper. Astronomers found the equivalent monstrosity in space: a near-record supermassive black hole that weighs 17 billion suns and lives in a cosmic backwater community of a few galaxies. Until now, extremely massive black holes have been found at the cores of very large galaxies in regions of the universe packed with other large galaxies. This is not just coincidence. Like a cosmic Pac-Man, a monster black hole gobbles smaller black holes when two galaxies collide. This game of bumper cars is common in large galaxy clusters. In fact, the current black hole record holder tips the scale at 21 billion suns and resides in the crowded Coma galaxy cluster, located 330 million light-years away.
The newly discovered supersized black hole resides in the center of a massive elliptical galaxy, NGC 1600, located in a small grouping of about 20 galaxies. Astronomers estimate that these smaller galactic groupings are about 50 times more abundant than spectacular galaxy clusters like the Coma cluster. Based on this discovery, astronomers are now asking, Is this the tip of an iceberg? Maybe there are more monster black holes out there that don't live in a skyscraper in Manhattan, but in a tall building somewhere in the Midwestern plains.
To learn even more about the behemoth black hole in galaxy NGC 1600, join astronomers and scientists during a live Hubble Hangout discussion at 3pm EDT on Thurs., April 7, at Supermassive Black Hole in an Unlikely Place.
Twenty-six candles grace NASA's Hubble Space Telescope's birthday cake this year, and now one giant space "balloon" will add to the festivities. Just in time for the 26th anniversary of Hubble's launch on April 24, 1990, the telescope has photographed an enormous, balloon-like bubble being blown into space by a super-hot, massive star. Astronomers trained the iconic telescope on this colorful feature, called the Bubble Nebula, or NGC 7635. The bubble is 7 light-years across – about one-and-a-half times the distance from our sun to its nearest stellar neighbor, Alpha Centauri. The Bubble Nebula lies 7,100 light-years from Earth in the constellation Cassiopeia.
Hubble Discovers Moon Orbiting the Dwarf Planet Makemake
Makemake is one of several dwarf planets that reside in the frigid outer realm of our solar system called the Kuiper Belt, a "junkyard" of countless icy bodies left over from our solar system's formation.
After discovering Makemake in 2005, astronomers had searched several times for a companion orbiting the icy world. Now, the Hubble Space Telescope has uncovered a tiny moon around Makemake that is estimated to be 100 miles wide. Nicknamed MK 2, the moon is more than 1,300 times fainter than Makemake, which is 870 miles across. MK 2 is 13,000 miles away from the dwarf planet.
Hubble Catches Views of a Jet Rotating with Comet 252P/LINEAR
For thousands of years, humans have recorded sightings of mysterious comets sweeping across the nighttime skies. These celestial wanderers, "snowballs" of dust and ice, are swift-moving visitors from the cold depths of space. Some of them periodically visit the inner solar system during their journeys around the sun.
Astronomers using NASA's Hubble Space Telescope captured images of Comet 252P/LINEAR just after it swept by Earth on March 21. The visit was one of the closest encounters between a comet and our planet. The comet traveled within 3.3 million miles of Earth, or about 14 times the distance between our planet and the moon. The images reveal a narrow, well-defined jet of dust ejected by the comet's icy, fragile nucleus. The jet also appears to change direction in the images, which is evidence that the comets nucleus is spinning. The spinning nucleus makes the jet appear to rotate like the water jet from a rotating lawn sprinkler. These observations also represent the closest celestial object Hubble has observed, other than the moon. The comet will return to the inner solar system again in 2021.
On May 12, 2016, astronomers using NASA's Hubble Space Telescope captured this striking image of Mars, when the planet was 50 million miles from Earth. The photo reveals details as small as 20 miles to 30 miles across. This observation was made just a few days before Mars opposition on May 22, when the sun and Mars will be on exact opposite sides of Earth. Mars also will be 47.4 million miles from Earth. On May 30, Mars will be the closest it has been to Earth in 11 years, at a distance of 46.8 million miles. Mars is especially photogenic during opposition because it can be seen fully illuminated by the sun as viewed from Earth.
NASA's Hubble Finds Universe Is Expanding Faster Than Expected
When astronomer Edwin Hubble discovered nearly 100 years ago that the universe was uniformly expanding in all directions, the finding was a big surprise. Then, in the mid-1990s, another shocker occurred: astronomers found that the expansion rate was accelerating perhaps due to a repulsive property called "dark energy." Now, the latest measurements of our runaway universe suggest that it is expanding faster than astronomers thought. The consequences could be very significant for our understanding of the shadowy contents of our unruly universe. It may mean that dark energy is shoving galaxies away from each other with even greater – or growing – strength. Or, the early cosmos may contain a new type of subatomic particle referred to as "dark radiation." A third possibility is that "dark matter," an invisible form of matter that makes up the bulk of our universe, possesses some weird, unexpected characteristics. Finally, Einstein's theory of gravity may be incomplete.
These unnerving scenarios are based on the research of a team led by Nobel Laureate Adam Riess, who began a quest in 2005 to measure the universe's expansion rate to unprecedented accuracy with new, innovative observing techniques. The new measurement reduces the rate of expansion to an uncertainty of only 2.4 percent. That's the good news. The bad news is that it does not agree with expansion measurements derived from probing the fireball relic radiation from the big bang. So it seems like something's amiss – possibly sending cosmologists back to the drawing board.
Pancake-shaped clouds not only appear in the children's book "Cloudy With a Chance of Meatballs," but also 3 billion miles away on the gaseous planet Neptune. When they appeared in July 2015, witnessed by amateur astronomers and the largest telescopes, scientists suspected that these clouds were bright companions to an unseen, dark vortex. The dark vortex is a high-pressure system where the flow of ambient air is perturbed and diverted upward over the vortex. This forms huge, lens-shaped clouds, that resemble clouds that sometimes form over mountains on Earth.
When NASA's Voyager 2 spacecraft flew by Neptune in 1989, astronomers were surprised to see such a gaping, dark hole at southern latitudes in the giant planet's cyan-colored atmosphere. The dark spot later disappeared. But the Hubble Space Telescope captured a new northern dark spot of comparable size in 1994. Hubble captured the appearance of a new dark spot on May 16, 2016. The spot would span the width of the continental United States.
Hubble Reveals Stellar Fireworks in 'Skyrocket' Galaxy
As we celebrate the Fourth of July by watching dazzling fireworks shows, another kind of fireworks display is taking place in a small, nearby galaxy.
A stellar fireworks show is lighting up one end of the diminutive galaxy Kiso 5639. The dwarf galaxy is shaped like a flattened pancake, but because it is tilted edge-on, it resembles a skyrocket, with a brilliant blazing head and a long, star-studded tail. Kiso 5639 is a rare, nearby example of elongated galaxies seen in abundance in the early universe. Astronomers suggest that the frenzied star birth is sparked by intergalactic gas raining on one end of the galaxy as it drifts through space.
Hubble Captures the Beating Heart of the Crab Nebula
At the center of the Crab Nebula, located in the constellation Taurus, lies a celestial "beating heart" that is an example of extreme physics in space. The tiny object blasts out blistering pulses of radiation 30 times a second with unbelievable clock-like precision. Astronomers soon figured out that it was the crushed core of an exploded star, called a neutron star, which wildly spins like a blender on puree. The burned-out stellar core can do this without flying apart because it is 10 billion times stronger than steel. This incredible density means that the mass of 1.4 suns has been crushed into a solid ball of neutrons no bigger than the width of a large city. This Hubble image captures the region around the neutron star. It is unleashing copious amounts of energy that are pushing on the expanding cloud of debris from the supernova explosion — like an animal rattling its cage. This includes wave-like tsunamis of charged particles embedded in deadly magnetic fields.
On July 4, 1054, Chinese astronomers recorded the supernova that formed the Crab Nebula. The ultimate celestial firework, this "guest star" was visible during the daytime for 23 days, shining six times brighter than the planet Venus. The supernova was also recorded by Japanese, Arabic, and Native American stargazers. While searching for a comet that was predicted to return in 1758, French astronomer Charles Messier discovered a hazy nebula in the direction of the long-vanished supernova. He would later add it to his celestial catalog as "Messier 1." Because M1 didn't move across the sky like a comet, Messier simply ignored it other than just marking it as a "fake comet." Nearly a century later the British astronomer William Parsons sketched the nebula. Its resemblance to a crustacean led to M1's other name, the Crab Nebula. In 1928 Edwin Hubble first proposed associating the Crab Nebula to the Chinese "guest star" of 1054.
