Tag Archives: star

Astronomers Solve Mystery Of Strange Object At The Center Of The Milky Way

G2, a mysterious object near the supermassive blackhole at the center of the galaxy, hosts what was once a pair of stars that have been merged by the enormous gravitational influence of their near neighbor.

Strange things happen at the center of galaxies. Black holes millions of times the mass of the sun produce enormous gravitational forces and emit x-rays. Stars crowd so close together, they are in danger of bumping into each other. Ionized streams of gas light up like auroras.

Yet even in such an intense environment, G2 is something special. It has puzzled astronomers, who initially suspected it of being a gas cloud approaching Sgr A*, the black hole at the galaxy’s center. Debate raged as to how much of it would survive the encounter

However, UCLA’s Professor Andrea Ghez challenged the assumption on which these ideas are based. G2, she argues in The Astrophysical Journal Letters, is not a gas cloud of roughly three Earth masses, as others have speculated, but instead contains a central star, one she suspects of a very interesting history.

Ghez’s conclusions are based on observations of G2 as it reached its closest approach (periapse) to Sgr A* in the course of its orbit. This happened earlier this year when G2 reached a distance of 3000 times the event horizon from Sgr A*. “It was one of the most watched events in astronomy in my career,” says Ghez.

A gas cloud lacking a central object, “should be tidally disrupted during periapse passage,” Ghez and her co-author’s suggest. However, using the 10m Keck telescopes and laser guide star adaptive optics to adjust for the effects of the Earth’s atmosphere, the authors found G2’s brightness and size remained the same and its orbital characteristics were consistent with a condensed object.

They propose the center of G2 is a star. “This star has a luminosity of ~30L? and is surrounded by a large (~2.6 AU) optically thick dust shell,” they argue.

Stars 30 times the brightness of the sun are not unusual; Vega and Sirius are a little above and below that respectively. However, Ghez says although we cannot see it directly, the team believe G2’s star is distinctive for its expansive size, the product of two stars merging together. This prompts an expansion that lasts around a million years before returning to a more normal diameter. 

“This may be happening more than we thought. The stars at the center of the galaxy are massive and mostly binaries,” syas Ghez. “It’s possible that many of the stars we’ve been watching and not understanding may be the end product of mergers that are calm now.”

The combination of the dense packing of stars at the galactic center, and the influence of Sgr A*’s gravity could cause stars to collide and join on a regular basis in a way that almost never happens in the outer reaches of the galaxy. G2’s collision occurred recently enough for us to see the process in action.

Read more: http://www.iflscience.com/space/solution-mystery-galaxys-heart

Rare Double Star System Seen In Final Death Throes Before It Explodes

An incredible stellar system has been found where two stars are so close that their surfaces are overlapping. It is the hottest and most massive double star system ever seen, and provides a rare glimpse into what is believed to be a relatively brief cosmic event.

The system is known as VFTS 352, found 160,000 light-years away in the Tarantula Nebula by the European South Observatory’sVery Large Telescope. Both of the stars are nearly identical in size, with a combined mass 57 times greater than the Sun, meaning one is not sucking material from the other rather, they are likely sharing 30% of their material. This has led to a bridge forming between their two connected surfaces.

The two stars, classed as O-type stars that shine blue-white, have surface temperatures of more than 40,000degrees Celsius(72,000degrees Fahrenheit), and complete an orbit of each other in just one Earth day. Double systems like this may be the main source of certain elements such as oxygen in the universe.

Their centers are separated by a mere 12 million kilometers (7.5 million miles), and the intense tidal forces (the gravitational pull of one star on the other) are thought to be mixing the material in their interiors. The VFTS 352 is the best case yet found for a hot and massive double star that may show this kind of internal mixing, said lead author Leonardo Almeida from the University of So Paulo, Brazil in a statement. As such its a fascinating and important discovery.

What will happen next to the stars is especially interesting. Its possible that the two may combine into a single giant star in 600,000 years that would spin extremely rapidly, and ultimately end in a huge explosion up to four million years later known as a long-duration gamma-ray burst, one of the most explosive events in the universe.

The other possibility is that the two will go supernova separately in about three million years, both becoming black holes but continuing to orbit one another, forming a binary black hole system. Such a remarkable object would be an intense source of gravitational waves, Selma de Mink of the University of Amsterdam, the lead theoretical astrophysicist on the team, said in the statement.

Whatever happens, this system is proving to be a fascinating insight into a rare and ethereal phenomenon.

Read more: http://www.iflscience.com/space/rare-double-star-system-seen-final-death-throes-it-explodes

North America To Scale On Various Planets In Our Solar System

We’ve all seen images comparing the size of Earth with that of other planets in the solar system. The problem, John Brady of Astronomy Central realized, is that these images assume a grasp of Earth’s scale. So Brady decided to do something different and compare astronomical objects with pieces of the planet his readers may be familiar with

Suddenly, with the huge continent of North America dwarfed by Jupiter’s storms, the universe seems an even larger place. In the other direction, Mars looks so much more human-scaled.

John Brady/Astronomy Central. How the U.S. and Canada would measure up to Mars.

Brady has also reversed the process, showing what the solar system’s largest mountain, Olympus Mons, would look like if it replaced the Grand Canyon as Arizona’s prime tourist attraction. At 26 kilometers (85,000 ft) high, it would truly be a wonder, since the Earth’s greater gravity restricts mountains to a third of that size or less.

John Brady/Astronomy Central. If located appropriately, Olympus Mons would cover the whole state of Arizona.

Not everything makes us feel small. If you live in Liverpool, UK, you might be tempted to go for a bike ride around the area that Brady shows would be encompassed by a neutron star, or make an equivalent image for your own home with the help of satellite photos.

John Brady/Astronomy CentralNeturon stars really are the size of a city.
Brady told the Huffington Post, “I got the ‘North America on Jupiter’ image to scale by looking at size comparisons on NASA images of Earth compared to Jupiter’s Great Red Spot. The Mars image with North America placed over it was done by knowing the diameter of the red planet, then finding the distance between two U.S. cities. I used New York and San Francisco.” 

Read more: http://www.iflscience.com/space/universe-north-american-scale

Astronomers Spot Massive Blue Stars Beginning To Merge

In the Giraffe constellation 13,000 light-years away, MY Camelopardalis is a massive binary system made up of two blue (that is, very hot and very bright) stars. They’re so close, they’re about to merge into a supermassive star—a process no one has ever seen before. Even though MY Cam is the first known example of a supermassive merger progenitor, astronomers studying the system say that most massive stars are created through mergers with smaller ones. The findings were published in Astronomy & Astrophysics last week.

Stars that move alone like our sun are the minority. Most stars in our galaxy were formed in binary or multiple systems, where they’re tied by gravity to a companion star. In some of these systems, the stars might appear to eclipse one another if their orbital planes face Earth. For that reason, MY Cam was thought to be a single star up until a decade ago.

Using observations from the Calar Alto Observatory in Spain, a team led by Javier Lorenzo from the University of Alicante found that the eclipsing binary MY Cam is made up of one star that’s 38 times the mass of our sun, and another that’s 32 solar masses. The two jumbo stars are very close together: Their orbital period is just under 1.2 days, making it the shortest orbital period known for these types of stars. In order to complete a full turn so quickly, the stars must be in extremely close contact (pictured above)—so close that they’re actually touching and their outer layer material are mixing together in what’s known as a common envelope. 

The members of this contact binary are moving around each other at a speed of over one million kilometers an hour. Additionally, the tidal forces in between make them rotate about themselves in just over a day—almost like Earth, except they each have a radius that’s 700 times bigger. The sun, by comparison, makes a full turn once every 26 days.

Not only is MY Cam the most massive eclipsing binary, it’s also the most massive binary with components so young they haven’t even begun to evolve, according to a news release. The stars are less than two million years old, National Geographic explains, and they were probably formed as we see them today. The researchers expect the two will merge into a single object that’s over 60 solar masses before either of them have had the time to evolve significantly. 

MY Cam sits at the end of the hindlegs of the Giraffe, and if you’re in the northern hemisphere, you could probably see it using just binoculars pointed between Ursa Major and Cassiopeia. 

Read more: http://www.iflscience.com/space/supermassive-merger-blue-stellar-giants-underway

Star Without Iron Inspires Galactic Archaeology

The most metal-poor star ever found is helping astronomers learn about the early universe in which it formed.

Just last month, astronomers announced that the star SDSS J001820.5-093939.2 showed signs of being spawned by early supernovae. As evidence, they noted that it has only 1/300th of the sun’s iron, and a distinctive pattern of deficient odd-numbered elements compared to those next to them on the periodic table.

While that research was taking place, a star with orders of magnitude less iron was found, bolstering the study of the first stars—a field that is sometimes refered to as “galactic archeology.”

The early universe lacked elements heavier than lithium. Most elements further along the periodic table have been produced in supernovae and then mixed into subsequent generations of stars. The concentrations of these elements reveal a lot about the explosions that preceded them. Iron is commonly used as a shorthand measure for heavier elements in general.

So to discover a star that has no measurable iron spectral lines at all was truly a surprise. The iron of SMSS J031300.36-670839.3 cannot be more than one ten-millionth of that of the sun. This is a hundredth the concentration of the previous record-breaking star. “We received the news of the most iron-poor star with a great excitement,” says Ken’ichi Nomoto of the University of Tokyo, “since this star may be the oldest fossil record and may elucidate the unknown nature of the first stars.” 

“The impact of stars on the surrounding environment depends critically on their masses when they were born,” says team leader Miho N. Ishigaki, also of Tokyo University. “However, direct observational constraints of the first stars’ masses are not available since most of them likely died out a long, long time ago.” 

Although SMSS J031300.36-670839.3 has almost no iron or calcium, it does have quite a lot of carbon. Ishigaki and Nomoto modeled the sort of supernova explosion required to leave the surrounding region with plenty of carbon but little else.

In The Astrophysical Journal, they propose that a star with between 25 and 40 times the mass of the sun exploded in a highly asymmetric fashion, with a huge jet expelling the contents of the star’s core in such a way that these elements fell back into the remnant black hole. On the other hand, the outer layers of the star—which would have been rich in carbon—were pushed out in all directions, enriching the surrounding gasses and becoming incorporated into stars such as SMSS J031300.36-670839.3.

“If such supernovae are actually possible,” Nomoto says, “the result supports the theoretical prediction that the first stars could be typical massive stars rather than monster-like objects with masses more than several hundred times that of the sun.”

There is great debate as to whether or not the first stars were much larger than anything that can exist in the universe today. While his work suggests that may not have always been the case, Ishigaki acknowledges there may have been a range of star sizes at the time.

 

 

Read more: http://www.iflscience.com/space/star-without-iron-galactic-archaeologists-dream

Astronomers Use “Light Echo” To Measure Size Of Star’s Disk

Scientists have used a rather novel technique to measure the size of the planet-forming disk of dust and gas surrounding a star near Earth.Using two telescopes, astronomers measured the time it took for light to travel from the star YLW 16B to Earth, and the time taken for the echo of this lightto bounceoff the disk.

This technique has allowed astronomers to calculate the distance of the star to its disk, which they estimate at 0.08 astronomical units (AU, 1 AU is the Earth-Sun distance), or 8 percentof Earths distance to the Sun.

This finding, published in the Astrophysical Journal, will allowus to get a better understanding of how planets form in these protoplanetary disks. Such disks are known to produce planets around stars, as objects scoop up material and sweep out gaps. But exactly how some planets form,such as hot Jupitersgas giants that form extremely close to their starsremains a mystery.

“Understanding protoplanetary disks can help us understand some of the mysteries about exoplanets, the planets in solar systems outside our own,” said lead author Huan Meng from the University of Arizona in a statement. “We want to know how planets form and why we find large planets called ‘hot Jupiters’ close to their stars.”

Above, a graphic showing how the measurement was made.NASA/JPL-Caltech

To make the measurement of this gap required a bit of trickery from the astronomers, though. At 400 billion light-years away, its difficult to make a direct visible observation because of the dust and gas surrounding the star.

However, YLW 16B is known to be a variable star, which means that it is often and irregularly changing in brightness. This is because it is still near the start of its life, having formed just 1million years ago (compared to 4.6 billion years for our Sun). When the star has one of its outbursts, we can detect this change in brightness.

But the change also means that the echo,produced by light bouncing off the protoplanetary disk, will be noticeably different. Using ground-based observatories, the team were able to measure the light from the star, and 74 seconds later, they used NASAs Spitzer space telescope to measure infrared light from the disk’secho. This gave them their measurement of 0.08 AUfor the gap.

The astronomers now think this method could be used to measure disks around other stars, giving us a better grasp on how weird and wonderful planets form.

Photo Gallery

Read more: http://www.iflscience.com/space/astronomers-use-light-echo-measure-size-stars-disk

Astronomers Have Discovered The Oldest Stars In Our Galaxy

An international team of astronomers has discovered some of the oldest stars in the Milky Way.In the process, they were able to learna lot about the abundance of different elements in the very early universe.

These stars, which are part of the second generation of stars to form in the universe, were discovered near the very center of the Milky Way and they are believed to have started shining200 million years after the Big Bang. The scientists thinkthat their findings, published in Nature,give an indication ofthe life and death of the very first stars.

The first stars are believed to have been huge, havingup to 1,000 times the mass of the Sun. It is thought that when these objects reached the end of their lives, they exploded inhypernova explosions,tens of times stronger than the supernovae we see in the universe today.The first generation havenot been directly observed yet, but astronomers hope to see them when the James Webb Space Telescope(JWST) starts operation in 2018.

The second generation, including the stars from this study, are metal-poor: They are made almost exclusively of helium and hydrogen, with only traces of heavier elements (the metals). The more metal a star has, the quicker it forms and the smaller it is.

After the Big Bang, the universe was composed of just hydrogen and helium. This is why the first-generation stars were so big.The carbon in our bodies, the oxygen in the air and all the other heavy elements we find in the universe were formed by the first two generations of stars.

The discovery didnt come easy. There are millions of stars in the Milky Ways bulge, so the team had to develop a strategy to make the gargantuan task of observing them in detailmore manageable.

Since very metal-poor stars are slightly bluer than other stars, the researchersselected 14,000 promising stars from the ANU SkyMapper telescope in Australia. Only 23 of themwerethen studied inmore detail in follow-up observations.

There are so many stars in the centerof our galaxy finding these rare stars is really like looking for a needle in a haystack, said co-authorDrAndrew Casey of Cambridges Institute of Astronomy in a statement. But if we select these stars in the right way, its like burning down the farm and sweeping up the needles with a magnet.

The elements released by the first stars act as a chemical signature that is still present in the stars observed in the study.

This work confirms that there are ancient stars in the centre of our galaxy. The chemical signature imprinted on those stars tells us about an epoch in the universe thats otherwise completely inaccessible, said Casey. The universe was probably very different early on, but to know by how much, weve really just got to find more of these stars: more needles in bigger haystacks.

Read more: http://www.iflscience.com/space/discovery-ancient-stars-sheds-light-primordial-hypernovae

New Massive Stars Spotted by Hubble

Most of the biggest and brightest stars we have ever observed are packed in a cluster not even 170,000 light-years away from us. And now, Hubble hasspotted even more giant stars in the group.

The space telescope has identified nine huge stars with masses over 100 times the mass of the Sun in the star cluster R136, which is located in the Large Magellanic Cloud. Together these ninestars are 30 million times brighter than the Sun. The results are published in theMonthly Notices of the Royal Astronomical Society,

The team also found dozens of 50-solar-massstars in the cluster, all packed into an area a few light-years in diameter. The observations were made possible by the lastupgrade performed on Hubble in 2009, which dramatically improved the spatial resolution in the ultraviolet by repairing the Space Telescope Imaging Spectrograph (STIS). These bright, big stars are ultraviolet powerhouses, so Hubble has finally been able to resolve them individually.

“The ability to distinguish ultraviolet light from such an exceptionally crowded region into its component parts, resolving the signatures of individual stars, was only made possible with the instruments aboard Hubble,” explainedPaul Crowther from the University of Sheffield,lead author of the study, in astatement.

“Together with my colleagues, I would like to acknowledge the invaluable work done by astronauts during Hubble’s last servicing mission: They restored STIS and put their own lives at risk for the sake of future science!”

Shown is the cluster R136 asseen in the ultraviolet.ESA/Hubble, NASA, K.A. Bostroem (STScI/UC Davis)

R136 hosts the largest, brightest star ever observed, R136a, which has a mass of 265 Suns and is 8.7 million times the luminosity of our own star. This star and three more with a mass of 150 solar masses were discovered by Crowther and his collaborators in 2010. The observations are incredible, but how these stellar behemoths form is still very mysterious.

“These newly found stars are pushing the theoretical limits of what is possible in terms of a stars existence,” saidDr. Chris Pearson, an RAL Space astronomer at Harwell Campus in theU.K., in a comment sent to IFLScience.Due to their size, they will burn much faster and brighter than our Sun, meaning they will have significantly shorter lifespans measured in millions rather than billions of years.

This researchis a significant step forward in our understanding, but theteam will continue observing this cluster in the hope of finding more clues on how these starsform.

“Once again, our work demonstrates that, despite being in orbit for over 25 years, there are some areas of science for which Hubble is still uniquely capable,” said Crowther.

Photo Gallery

Read more: http://www.iflscience.com/space/new-massive-stars-spotted-hubble

Scientists Can Tell How Old A Star Is Based On How Fast It’s Spinning

Unlike humans, stars don’t have to put any effort into concealing their age—they are notoriously, and frustratingly, good at it. But we do share one thing in common: Stars slow down as they get older, a feature that scientists have been taking advantage of for some years now. However, with a limited data set, scientists have struggled to make reliable calculations.

Now, thanks to Kepler observations, scientists have finally demonstrated that they can accurately determine the age of sun-like stars from how fast they are spinning. Their work, which has been presented at a meeting of the American Astronomical Society, represents a giant leap towards the ultimate goal of building a clock that can precisely measure the ages of stars from their spins.

Learning the age of a star is crucial for many astronomical studies, in particular for the search of planets outside our solar system (exoplanets), and of course extraterrestrial life. Given that stars and planets form together, if we know the age of a star, we can determine the age of its planets. And the older the planet, the greater the possibility of finding life as it has had more time to get started.

Scientists are particularly interested in stars like our own, or “cool stars.” These are the most abundant stars in our galaxy and are also very bright. These galactic lamp posts also host the majority of Earth-like planets spotted so far. Unfortunately, these stars are tricky to age because their size and brightness don’t change much throughout most of their lives. But scientists have identified something that does change as a star grows old: its rotation, which gradually gets slower.

According to the new work, there is a close relationship between a star’s mass, spin and age, and if the first two can be measured, the third can be calculated. To measure a star’s spin, scientists look at dark patches, called star spots, which travel across the surface as it rotates. When astronomers look at distant stars, they can’t directly see these spots, so instead they look for dips in brightness that occur when the spot appears.

Typically, these spots only dim a star’s brightness by less than 1%, meaning the changes are very difficult to measure. This is where NASA’s Kepler spacecraft came to the rescue, which has provided precise measurements of stellar brightness since 2009.

In order to calibrate their stellar clock, scientists needed to measure the spin periods of stars with known ages and masses. Prior to this study, this had only been achieved for stars within a 1-billion-year-old cluster NGC 6811, which rotated about once every 10 days, and of course for our own 4.6 billion year old sun, which had a spin period of 26 days. Now, scientists have added to this data set by measuring the spin of 30 sun-like stars in a cluster known to be 2.5 billion years old, closing a “four-billion-year-gap.” As described in Nature, the stars in this cluster, NGC 6819, sat beautifully in this gap, rotating around every 18 days.

Prior to this work, the ages of cool stars came with a margin of error as large as 100%; now, this has been reduced to around 10%.

[Via Harvard CfA, Nature and BBC News]

Read more: http://www.iflscience.com/space/scientists-age-stars-based-their-spin

NASA Releases Stunning Half-Hour Ultra HD Video Of The Sun

NASA has created its first few ultra-high definition videos, and the results are truly spectacular. Among the items released is a jaw-dropping 30-minute portrait of the Sun, which was put together from data captured by the Solar Dynamics Observatory (SDO).

Launched in early 2010, the SDO observes the Sun around the clock, capturing images in ten different wavelengths, each of which highlights a different temperature of solar material.By observing these multiple types of radiation, NASA is able to keep tracks on a number of facets of solar activity, such as solar flares and streams of electrified plasma called coronal loops.

By putting it all together in stunning 4K resolution, NASA has created an image of the Sun as youve never seen it before.

Read more: http://www.iflscience.com/space/stunning-HD-video-of-sun