These Ancient Stars May Be the Oldest Ever Seen in the Milky Way


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These Ancient Stars May Be the Oldest Ever Seen in the Milky Way

 These Ancient Stars May Be the Oldest Ever Seen in the Milky Way
An artist’s illustration of a hypernova, a star explosion 10 times more powerful than a regular supernova. The first stars to ignite would have died in explosions like these, scientists say.

Credit: European Southern Observatory

Astronomers have found what may be the oldest stars in the Milky Way. The stars, discovered in the galaxy’s bulge, reveal that extraordinarily powerful explosions known as hypernovas might have dominated the Milky Way during its youth, researchers say.

The oldest stars in the universe are poor in what astronomers call “metals” — elements heavier than helium. When these stars died in giant outbursts known as supernovas, they released these metals into the cosmos, and each succeeding generation of stars is generally more metal-rich than the last.

Previous research suggested the first stars formed about 13.6 billion years ago, within 200 million years of the Big Bang, initiating what scientists call the cosmic dawn. Astronomers have not yet discovered a first star, but extremely metal-poor stars that were probably immediate successors of the first stars have been seen in the outer regions, or “halo,” of the Milky Way. [Watch: The Universe’s Oldest Stars May Be Close to Us]

Still, prior studies indicated that extremely metal-poor stars should mostly be found not in the halos of galaxies, but in their central regions, or “bulges.” Galactic bulges are loaded with gas and dust — the building blocks from which stars are born.

The bulge of our Milky Way galaxy is packed with stars and dust as seen in this image taken by the SkyMapper telescopes at Australia's Siding Spring Observatory during the EMBLA astronomical survey.

The bulge of our Milky Way galaxy is packed with stars and dust as seen in this image taken by the SkyMapper telescopes at Australia’s Siding Spring Observatory during the EMBLA astronomical survey.

Credit: Christopher Owen

Until now, astronomers had not detected any extremely metal-poor stars in the Milky Way’s bulge, in part because Earth is located in the Milky Way’s halo, and the bulge is very far away, with a lot of intervening dust obscuring Earth’s view of the bulge.

In addition, the vast majority of the stars in the Milky Way’s bulge are metal-rich. Because the bulge is dense with gas and dust, star formation happened quickly there, and when the galaxy’s early stars died, they enriched their surroundings with heavier elements within the first 1 billion to 2 billion years of the universe. This makes finding extremely metal-poor stars in the Milky Way’s bulge “like searching for a needle in a haystack,” said study lead author Louise Howes, an astronomer now at Lund University in Sweden, who carried out this research while at Australian National University in Canberra.

Now, Howes and her colleagues have, for the first time, identified stars from the cosmic dawn in the Milky Way’s bulge.

“These are the oldest stars that have ever been found in the Milky Way,” Howes told Space.com.

The researchers used the Australian National University’s SkyMapper telescope to scan about 5 million stars in the Milky Way’s bulge. They focused on the fingerprints of elements in the stars, which appear as distinct lines in the spectrum of their light.

This photo shows the SkyMapper telescope at Siding Spring Observatory in Australia, which scientists used to observe more than 5 million stars in a survey that found evidence of the oldest stars in the Milky Way.
This photo shows the SkyMapper telescope at Siding Spring Observatory in Australia, which scientists used to observe more than 5 million stars in a survey that found evidence of the oldest stars in the Milky Way.

Credit: James Gilbert

After using SkyMapper to discover more than 14,000 potential extremely metal-poor stars, the scientists used the Australian Astronomical Observatory’s Anglo-Australian Telescope to confirm that more than 500 of these stars were extremely metal-poor, each possessing less than one-hundredth the amount of iron seen in the sun. As expected, most of the extremely metal-poor stars that astronomers now know about are found in the galaxy’s bulge instead of its center.

Using the Magellan Clay telescope at the Las Campanas Observatory in Chile, the astronomers closely analyzed 23 of the most metal-poor bulge stars to determine their chemical composition. Oddly, the researchers found that these bulge stars were as poor in carbon as they were in iron. In contrast, metal-poor stars in the galaxy’s halo are often rich in carbon, possessing as much as the sun does.

“That’s surprising — it’s goes against what was predicted,” Howes said.

These findings suggest that the earliest stars might not have died in normal supernovas, but in titanic explosions known as hypernovas, which are 10 times more powerful than regular supernovas.

“This work really changes our ideas of what the first stars would have looked like, and how they would have developed and died, and how the galaxy would have evolved, and also sheds light on the formation of all the elements in the universe,” Howes said.

This research analyzed only one-third of the part of the sky that the Milky Way’s bulge covers. Future research could analyze the rest of the bulge that astronomers can see, so they can learn more about the metal-poor stars there, Howes said.

The scientists detailed their findings online Nov. 11 in the journal Nature.

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Image of the Day


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Image of the Day

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Great Pyramids Seen From Space

Credit: ESA

Gas Giants: Facts About the Outer Planets


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Gas Giants: Facts About the Outer Planets

The planets of the solar system as depicted by a NASA computer illustration. Orbits and sizes are not shown to scale.

Credit: NASA

A gas giant is a large planet composed mostly of gases, such as hydrogen and helium, with a relatively small rocky core. The gas giants of our solar system are Jupiter, Saturn, Uranus and Neptune. These four large planets, also called jovian planets after Jupiter, reside in the outer part of the solar system past the orbits of Mars and the asteroid belt. Jupiter and Saturn are substantially larger than Uranus and Neptune, and each pair of planets has a somewhat different composition.

Although there are only four large planets in our solar system, astronomers have discovered thousands outside of it, particularly using NASA’s Kepler Space Telescope. These exoplanets (as they are called) are being examined to learn more about how our solar system came to be.

Jupiter is the largest planet in our solar system. It has a radius almost 11 times the size of Earth. It has 50 known moons and 17 waiting to be confirmed,according to NASA. The planet is mostly made of hydrogen and helium surrounding a dense core of rocks and ice, with most of its bulk likely made up of liquid metallic hydrogen, which creates a huge magnetic field. Jupiter is visible with the naked eye and was known by the ancients. Its atmosphere consists mostly of hydrogen, helium, ammonia and methane. [Related: Planet Jupiter: Facts About Its Size, Moons and Red Spot]

Saturn is about nine times Earth’s radius and is characterized by large rings; how they formed is unknown. It has 53 known moons and nine more awaiting confirmation, according to NASA. Like Jupiter, it is mostly made up of hydrogen and helium that surround a dense core and was also tracked by ancient cultures. Its atmosphere is similar to Jupiter’s. [Related: Planet Saturn: Facts About Saturn’s Rings, Moons & Size]

Uranus has a radius about four times that of Earth’s. It is the only planet tilted on its side, and it also rotates backward relative to every planet but Venus, implying a huge collision disrupted it long ago. The planet has 27 moons, and its atmosphere is made up of hydrogen, helium and methane, according to NASA. It was discovered by William Herschel in 1781. [Related: Planet Uranus: Facts About Its Name, Moons & Orbit]

Neptune also has a radius about four times that of Earth’s. Like Uranus, its atmosphere is mostly made up of hydrogen, helium and methane. It has 13 confirmed moons and an additional one awaiting confirmation, according to NASA. It was discovered by several people in 1846. [Related: Planet Neptune: Facts About Its Orbit, Moons & Rings]

Super-Earths: Scientists have found a multitude of “super-Earths” (planets between the size of Earth and Neptune) in other solar systems. There are no known super-Earths in our own solar system, although some scientists speculate there may be a “Planet Nine” lurking in the outer reaches of our solar system. Scientists are studying this category of planets to learn whether super-Earths are more like small giant planets or big terrestrial planets.

Astronomers think the giants first formed as rocky and icy planets similar toterrestrial planets. However, the size of the cores allowed these planets (particularly Jupiter and Saturn) to grab hydrogen and helium out of the gas cloud from which the sun was condensing, before the sun formed and blew most of the gas away.

Since Uranus and Neptune are smaller and have bigger orbits, it was harder for them to collect hydrogen and helium as efficiently as Jupiter and Saturn. This likely explains why they are smaller than those two planets. On a percentage basis, their atmospheres are more “polluted” with heavier elements such as methane and ammonia because they are so much smaller.

Scientists have discovered thousands of exoplanets. Many of these happen to be “hot Jupiters,” or massive gas giants that are extremely close to their parent stars. (Rocky worlds are more abundant in the universe, according to estimates from Kepler.) Scientists speculate that large planets may have moved back and forth in their orbits before settling into their current configuration. But how much they moved is still a subject of debate.

There are dozens of moons around the giant planets. Many formed at the same time as their parent planets, which is implied if the planets rotate in the same direction as the planet close to the equator (such as the huge Jovian moons Io, Europa, Ganymede and Callisto.) But there are exceptions.

One moon of Neptune, Triton, orbits the planet opposite to the direction Neptune spins — implying that Triton was captured, perhaps by Neptune’s once larger atmosphere, as it passed by. And there are many tiny moons in the solar system that rotate far from the equator of their planets, implying that they were also snagged by the immense gravitational pull.

Jupiter: NASA’s Juno spacecraft arrived at the planet in 2016 and has already made several discoveries. It studied the planet’s rings, which is difficult to achieve since they are far subtler than Saturn’s. Juno discovered that the particles influencing the auroras of Jupiter are different than those on Earth. It also revealed insights about the atmosphere, such as finding snow emanating from high-altitude clouds. Meanwhile, scientists using the Hubble Space Telescope have made detailed studies of Jupiter’s Great Red Spot, watching it shrink and intensify in color.

Saturn: The Cassini spacecraft wrapped up more than a dozen years of observation at Saturn in 2017. But the science Cassini performed is still very much in progress, as scientists analyze work from its many years at Saturn. In its latter months, the mission examined Saturn’s gravity and magnetic fields, looked at the rings from a different angle than before, and plunged into the atmosphere deliberately (a move that will reveal more about the structure of the atmosphere.)

Uranus: The storms of Uranus are a frequent target for both professional telescopes and amateur astronomers, who monitor how they evolve and change over time. Scientists are also interested in learning about the structure of its rings, and what its atmosphere is made of. Uranus may also have several Trojan asteroids (asteroids in the same orbit as the planet); the first was found in 2013.

Neptune: Storms on Neptune are also a popular observing target, and in 2018 those observations again bore fruit; work from the Hubble Space Telescope showed that a long-standing storm is now shrinking. The researchers noted the storm is dissipating differently than what their models expected, which shows that our understanding of Neptune’s atmosphere still requires refinement.

Exoplanets: Many ground telescopes search for exoplanets. There are also several active space missions performing exoplanet research, including Kepler, the Hubble Space Telescope and the Spitzer Space Telescope. A flurry of new missions is also planned: the NASA Transiting Exoplanet Survey Satellite (TESS) in 2018, the NASA James Webb Space Telescope in 2020, the European Space Agency’s PLAnetary Transits and Oscillations of stars (PLATO) in 2026 and ESA’s Atmospheric Remote-sensing Infrared Exoplanet Large-survey mission (Ariel) in 2028.

Chinese Space Station Is Tumbling Toward an Easter Sunday Crash


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Chinese Space Station Is Tumbling Toward an Easter Sunday Crash

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ARLINGTON, Va. – The falling Chinese space station Tiangong-1 is tumbling in orbit and may crash back to Earth early Easter Sunday (April 1), experts say.Estimates for the crash of Tiangong-1 range sometime between March 31 and April 1, with a focus of 10 a.m. EDT (1400 GMT) on April 1, according to Aerospace Corp., which is tracking the space lab’s fall. That April 1 target comes with an error of 16 hours, so the spacecraft could potentially begin its fiery death dive anytime between Saturday and Sunday afternoon. An analysis by the European Space Agency also supports that re-entry estimate. [China’s Falling Tiangong-1: What You Need to Know]

An artist's illustration of China's Tiangong-1 space station as it breaks apart and burns up in Earth's atmosphere.

An artist’s illustration of China’s Tiangong-1 space station as it breaks apart and burns up in Earth’s atmosphere.

Credit: Aerospace Corporation

But scientists and engineers still cannot pinpoint exactly where and when the 9.4-ton (8.5 metric tons) space station will fall. Partly that is because the school bus-size Tiangong-1 is tumbling as it falls, which makes it hard to predict how atmospheric drag will affect the spacecraft’s re-entry time and path, Aerospace Corp. engineers said Wednesday (March 28).

“It is tumbling,” Roger Thompson, a senior engineering specialist with Aerospace Corp., told reporters at the company’s office here Wednesday. “We have been able to confirm that there is a tumble, we just can’t tell the orientation.”

Aerospace Corp. confirmed using U.S. Air Force radar data and telescope observations, Thompson said.

This map by the European Space Agency shows the area in which China's Tiangong-1 space station could fall (shown in green) around April 1, 2018.

This map by the European Space Agency shows the area in which China’s Tiangong-1 space station could fall (shown in green) around April 1, 2018.

Credit: European Space Agency

Tiangong-1 launched in September 2011 to test docking systems and other technology needed for an even larger, multi-module space station to be built in the 2020s. The station was visited by China’s uncrewed Shenzhou-8 spacecraft in November 2011 and two crewed missions, one each in 2012 and 2013, respectively.

In March 2016, Tiangong-1 stopped communicating with its mission control center in Beijing, leading the China Manned Space Engineering Office (CMSEO) to declare its mission over. Tiangong-1 has been space junk ever since.

Currently, Tiangong-1 is expected to fall to Earth somewhere between the latitudes of 42.7 degrees north and 42.7 degrees south, a range that spans the border of South Dakota and Nebraska in the north and Tasmania in the south.

As re-entry day nears for Tiangong-1, satellite trackers will be able to make more refined predictions for where and when it will crash. In a statement today (March 29), CMSEO officials said the public should not fear being hit by debris from Tiangong-1.

“There is no need for people to worry about its re-entry into the atmosphere. It won’t crash to the Earth fiercely, as in sci-fi movie scenarios, but will look more like a shower of meteors,” the statement said according to the state-run Xinhua news service.

You can still see the Tiangong-1 space station in the night sky, if you know when and where to look and have good weather.

In fact, the chances of being struck by debris from Tiangong-1 are less than 1 in a trillion, according to a fact sheet from Aerospace Corp.

If you are able to see the Tiangong-1 re-entry, you can report your sighting to Aerospace Corp.’s Center for Orbital and Reentry Debris Studies through the CORDS website here.

Email Tariq Malik at tmalik@space.com or follow him @tariqjmalik. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.