Artist's impression of the Earth scorched by our Sun as it enters its Red Giant Branch phase. Credit: Wikimedia Commons/Fsgregs
It’s amazing what astronomers can figure out from afar, and this now might include whether a star ate a few planets sometime during its history. Through looking at the predicted elements that make up a star, and any changes, this could be a key to figuring out if any planets were swallowed up by the star.
“Imagine that the star originally formed rocky planets like Earth. Further, imagine that it also formed gas giant planets like Jupiter,” stated Trey Mack, a graduate student in astronomy at Vanderbilt University who led the research.
“The rocky planets form in the region close to the star where it is hot and the gas giants form in the outer part of the planetary system where it is cold. However, once the gas giants are fully formed, they begin to migrate inward and, as they do, their gravity begins to pull and tug on the inner rocky planets. If enough rocky planets fall into the star, they will stamp it with a particular chemical signature that we can detect.”
Stars are mostly made up of hydrogen and helium (98%), meaning other elements only make up about 2% of the star. These elements (all of which are heavier than hydrogen and helium) are referred to as metals and when it comes to iron abundance, you will sometimes see the term “metallicity” referred to, concerning the ratio of iron to hydrogen.
To expand on previous studies concerning metallicity and how planets form, Mack examined sun-like stars to see the abundance of 15 elements, especially those such as aluminum, silicon, calcium and iron — considered to be the foundation of rocky planets such as the Earth.
The astronomers examined binary sun-like stars HD 20781 and HD 20782, which started with the same chemical compositions since they both came to be in the same gas and dust cloud. One star hosts two Neptune-sized planets, while the other has a Jupiter-sized planet.
“When they analyzed the spectrum of the two stars, the astronomers found that the relative abundance of the refractory elements was significantly higher than that of the Sun,” Vanderbilt University stated. “They also found that the higher the melting temperature of a particular element, the higher was its abundance, a trend that serves as a compelling signature of the ingestion of Earth-like rocky material.”
One of these stars (the one with the Jupiter-sized planet) probably ate up 10 Earth masses while the other star ate about 20 Earth masses. Between the star’s chemical composition and the fact that the gas giants are either in close or eccentric orbits, this implies there would be no rocky planets in the systems. More generally, if other stars are found to meet up with these explanations, this could be a clue to finding rocky planets.
“When we find stars with similar chemical signatures, we will be able to conclude that their planetary systems must be very different from our own, and that they most likely lack inner rocky planets,” added Mack. “And when we find stars that lack these signatures, then they are good candidates for hosting planetary systems similar to our own.”
Artist's conception of a hyperveloctiy star heading out from a spiral galaxy (similar to the Milky Way) and moving into dark matter nearby. Credit: Ben Bromley, University of Utah
Zoom! A star was recently spotted speeding at 1.4 million miles an hour (2.2 million km/hr), which happened to be the closest and second-brightest of the so-called “hypervelocity” stars found so far.
Now that about 20 of these objects have been found, however, astronomers are now trying to use the stars beyond classifying them. One of those ways could be probing the nature of dark matter, the mysterious substance thought to bind together much of the universe.
LAMOST-HVS1 (as the object is called, after the Chinese Large Sky Area Multi-Object Fiber Spectroscopic Telescope that discovered it) is about three times faster than most other stars found. It’s in a cluster of similar hypervelocity stars above the Milky Way’s disk and from its motion, scientists suspect it actually came from our galaxy’s center.
What’s interesting about the star, besides its pure speed, is it is travelling in a “dark matter” halo surrounding our galaxies, the astronomers said.
The Milky Way is a spiral galaxy with several prominent arms containing stellar nurseries swathed in pink clouds of hydrogen gas. The sun is shown near the bottom in the Orion Spur. Credit: NASA
“The hypervelocity star tells us a lot about our galaxy – especially its center and the dark matter halo,” stated Zheng Zheng, an astronomy researcher at the University of Utah who led the study.
“We can’t see the dark matter halo, but its gravity acts on the star. We gain insight from the star’s trajectory and velocity, which are affected by gravity from different parts of our galaxy.”
The star is about 62,000 light years from the galaxy’s center (much further than the sun’s 26,000 light years) and is about four times hotter and 3,400 times brighter than our own sun. Astronomers estimate it is 32 million years old, which makes it quite young compared to the sun’s 4.5 billion years.
Image of a hypervelocity star found in data from the Sloan Digital Sky Survey. Image via Vanderbilt University.
Readers of Universe Today may also recall a “runaway star cluster” announced a few weeks ago, which shows you that the universe is replete with speeding objects.
“If you’re looking at a herd of cows, and one starts going 60 mph, that’s telling you something important,” stated Ben Bromley, a fellow university professor who was not involved with Zheng’s study. “You may not know at first what that is. But for hypervelocity stars, one of their mysteries is where they come from – and the massive black hole in our galaxy is implicated.”
The study was recently published in Astrophysical Journal Letters.
Location chart for HD 162826, considered a sibling to the sun. Credit: Ivan Ramirez/Tim Jones/McDonald Observatory
Peer about 110 light-years away from our solar system, and you might catch a glimpse of how our own neighborhood came together. The recent discovery that HD 162826 — a star bright enough to be seen in binoculars — could be a “sibling” of our sun could shed more light on the solar system’s formation, astronomers said.
“We want to know where we were born,” stated Ivan Ramirez, an astronomer at the University of Texas at Austin who led the research. “If we can figure out in what part of the galaxy the sun formed, we can constrain conditions on the early solar system. That could help us understand why we are here.”
The star is called a “sibling” because it could have formed from the same gas and dust cloud in which our own solar system was formed, some 4.5 billion years ago. Since life is in our own solar system, a natural next question is whether HD 162826 could also have life-bearing planets. There is a tiny reason for “yes”, the astronomers said.
Basically, the argument goes that when the stars were first born and close together, chunks of matter could have been knocked off protoplanets and travelled between the two solar systems. There’s a small chance that this could have brought primitive life to Earth, although of course there’s a long way to go before that could even be proved.
This artist’s conception shows a newly formed star surrounded by a swirling protoplanetary disk of dust and gas. Credit: University of Copenhagen/Lars Buchhave
That said, no planets have yet been found around HD 162826. (The star was known before, but just recently identified as a “sibling.”) Separate studies by the University of Texas and University of South Wales said there are likely no “hot Jupiters” (Jupiter-sized planets close to the star) nor Jupiter-sized planet in the solar system even further away. Smaller terrestrial planets, however, would have escaped the notice of this particular study.
The star is about 15 percent more massive than our sun and was selected from a list of 30 candidates based on its chemistry and orbit. There could also be more siblings out there to find, with one potential big help coming soon: the Gaia survey from the European Space Agency launched in December, which will chart the Milky Way in three dimensions.
Because Gaia will showcase the distance and motions of a billion stars, this will allow astronomers to look for these “solar siblings” as far in as the galaxy’s center, increasing the number of stars studied by a factor of 10,000. The exciting thing, the astronomers add, is with enough stars pinpointed as siblings to our sun, their orbits can then be traced back to the origin point — showing the location in the cosmos where the sun first came to be.
More information will be available in the June 1 issue of the Astrophysical Journal. A preprint version is available on Arxiv.
Artist's conception of a starquake cracking the surface of a neutron star. Credit: Darlene McElroy of LANL
Much like how an earthquake can teach us about the interior of the Earth, a starquake shows off certain properties about the inside of a star. Studying the closest star we have (the sun) has yielded information about rotation, radius, mass and other properties of stars that are similar to our own. But how do we apply that information to other types of stars?
A team of astronomers attempted to model the inside of a delta-Scuti, a star like Caleum that is about 1.5 to 2.5 times the mass of the sun and spins rapidly, so much more that it tends to flatten out. The model reveals there is likely a correlation between how these types of stars oscillate, and what their average density is. The theory likely holds for stars as massive as four times the mass of our sun, the team said.
“Thanks to asteroseismology we know precisely the internal structure, mass, radius, rotation and evolution of solar type stars, but we had never been able to apply this tool efficiently to the study of hotter and more massive stars,” stated Juan Carlos Suárez, a researcher at the Institute of Astrophysics of Andalusia who led the investigation.
Model of an oscillation within the sun. Credit: David Guenther, Saint Mary´s University
What’s more, knowing how dense a star is leads to other understandings: what its mass is, its diameter and also the age of any exoplanets that happen to be hovering nearby. The astronomers added that the models could be of use for the newly selected Planetary Transits and Oscillations (PLATO) telescope that is expected to launch in 2024.
A portion of a collage of galaxies included in the Herschel Reference Survey, in false color to show different dust temperatures. (Blue is colder, and red is warmer). Credit: ESA/Herschel/HRS-SAG2 and HeViCS Key Programmes/L. Cortese (Swinburne University)
While dust is easy to ignore in small quantities (says the writer looking at her desk), across vast reaches of space this substance plays an important role. Stick enough grains together, the theory goes, and you’ll start to form rocks and eventually planets. On a galaxy-size scale, dust may even effect how the galaxy evolves.
A new survey of 323 galaxies reveals that dust is not only affected by the kinds of stars in the vicinity, but also what the galaxy is made of.
“These dust grains are believed to be fundamental ingredients for the formation of stars and planets, but until now very little was known about their abundance and physical properties in galaxies other than our own Milky Way,” stated lead author Luca Cortese, who is from the Swinburne University of Technology in Melbourne, Australia.
“The properties of grains vary from one galaxy to another – more than we originally expected,” he added. “As dust is heated by starlight, we knew that the frequencies at which grains emit should be related to a galaxy’s star formation activity. However, our results show that galaxies’ chemical history plays an equally important role.”
Galaxies in the Herschel Reference Survey in infrared/submillimeter wavelengths (with the Herschel space telescope, at left) and the Sloan Digital Sky Survey (right). Herschel’s false-color image shows galaxies with cold dust (blue) and warm dust (red). Sloan highlights young stars (blue) and old stars (red). “Together, the observations plot young, dust-rich spiral/irregular galaxies in the top left, with giant dust-poor elliptical galaxies in the bottom right,” the European Space Agency stated. Credit: ESA/Herschel/HRS-SAG2 and HeViCS Key Programmes/Sloan Digital Sky Survey/ L. Cortese (Swinburne University)
Data was captured with two cameras on the just-retired Herschel space telescope: Spectral and Photometric Imaging Receiver (SPIRE) and Photodetecting Array Camera and Spectrometer (PACS). These instruments examined different frequencies of dust emission, which shows what the grains are made of. You can see a few of those galaxies in the image above.
“The dust-rich galaxies are typically spiral or irregular, whereas the dust-poor ones are usually elliptical,” the European Space Agency stated. “Dust is gently heated across a range of temperatures by the combined light of all of the stars in each galaxy, with the warmest dust being concentrated in regions where stars are being born.”
Astronomers initially expected that a galaxy with speedy star formation would display more massive and warmer stars in it, corresponding to warmer dust in the galaxy emitting light in short wavelengths.
“However, the data show greater variations than expected from one galaxy to another based on their star formation rates alone, implying that other properties, such as its chemical enrichment, also play an important role,” ESA said.
A 2014 image of NGC 2174 by the Hubble Space Telescope. Credit: NASA/ESA and the Hubble Heritage Team (STScI/AURA)
Billowing gas clouds and young stars feature in this February Hubble Space Telescope image, released as the telescope approaches its 24th birthday this coming April. The telescope has seen a lot of drama over the years, but in this case, thankfully the excitement is taking place 6,400 light-years away. Here you can see starbirth in action in the nebula NGC 2174, which is sometimes called the Monkey Head Nebula.
“This region is filled with young stars embedded within bright wisps of cosmic gas and dust. Dark dust clouds billow outwards, framed against a background of bright blue gas. These striking hues were formed by combining several Hubble images taken through different coloured filters, revealing a broad range of colours not normally visible to our eyes,” the European Space Agency wrote.
“These vivid clouds are actually a violent stellar nursery packed with the ingredients needed for building stars. The recipe for cooking up new stars is quite inefficient, and most of the ingredients are wasted as the cloud of gas and dust disperses. This process is accelerated by the presence of fiercely hot young stars, which triggers high-speed winds that help to blow the gas outwards.”
Hubble’s dramatic history includes a deformed mirror, a rescue mission, and a nearly last-minute decision to do a shuttle flight for repairs and upgrades when the shuttle program was wrapping up. You can read more about Hubble’s colorful history at the Space Telescope Science Institute.
A recent analysis of a star in the south hemisphere constellation of Centaurus has highlighted the role that amateurs play in assisting with professional discoveries in astronomy.
The find used of the European Southern Observatory’s Very Large Telescope based in the Atacama Desert in northern Chile — as well as data from observatories around the world — to reveal the nature of a massive yellow “hypergiant” star as one of the largest stars known.
The stats for the star are impressive indeed: dubbed HR 5171 A, the binary system weighs in at a combined 39 solar masses, has a radius of over 1,300 times that of our Sun, and is a million times as luminous. Located 3,600 parsecs or over 11,700 light years distant, the star is 50% larger than the famous red giant Betelgeuse. Plop HR 5171 A down into the center of our own solar system, and it would extend out over 6 astronomical units (A.U.s) past the orbit of Jupiter.
The field around HR 5171 A (the brightest star just below center). Credit: ESO/Digitized Sky Survey 2.
Researchers used observations going back over 60 years – some of which were collected by dedicated amateur astronomers – to pin down the nature of this curious star. A variable star just below naked eye visibility spanning a magnitude range from +6.1 to +7.3, HR 5171 A also has a relatively small companion star orbiting across our line of sight once every 1300 days. Such a system is known as an eclipsing binary. Famous examples of similar systems are the star Algol (Alpha Persei), Epsilon Aurigae and Beta Lyrae. The companion star for HR 5171 is also a large star in its own right at around six solar masses and 400 solar radii in size. The distance from center-to-center for the system is about 10 A.U.s – the distance from Sol to Saturn – and the surface-to-surface distance for the A and B components of the system are “only” about 2.8 A.U.s apart. This all means that these two massive stars are in physical contact, with the expanded outer atmosphere of the bloated primary contacting the secondary, giving the pair a distorted peanut shape.
“The companion we have found is very significant as it can have an influence on the fate of HR 5171 A, for example stripping off its outer layers and modifying its evolution,” said astronomer Olivier Chesneau of the Observatoire de la Côte d’Azur in Nice France in the recent press release.
Knowing the orbital period of a secondary star offers a method to measure the mass of the primary using good old Newtonian mechanics. Coupled with astrometry used to measure its tiny parallax, this allows astronomers to pin down HR 5171 A’s stupendous size and distance.
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Along with luminous blue variables, yellow hypergiants are some of the brightest stars known, with an absolute magnitude of around -9. That’s just 16x times fainter than the apparent visual magnitude of a Full Moon but over 100 times brighter than Venus – if you placed a star like HR 5171 A 32 light years from the Earth, it would easily cast a shadow.
Astronomers used a technique known as interferormetry to study HR 5171 A, which involves linking up several telescopes to create the resolving power of one huge telescope. Researchers also culled through over a decade’s worth data to analyze the star. Though much of what had been collected by the American Association of Variable Star Observers (the AAVSO) had been considered to be too noisy for the purposes of this study, a dataset built from 2000 to 2013 by amateur astronomer Sebastian Otero was of excellent quality and provided a good verification for the VLT data.
The discovery is also crucial as researchers have come to realize that we’re catching HR 5171 A at an exceptional phase in its life. The star has been getting larger and cooling as it grows, and this change can be seen just over the past 40 year span of observations, a rarity in stellar astronomy.
“It’s not a surprise that yellow hypergiants are very instable and lose a lot of mass,” Chesneau told Universe Today. “But the discovery of a companion around such a bright star was a big surprise since any ‘normal’ star should at least be 10,000 times fainter than the hypergiant. Moreover, the hypergiant was much bigger than expected. What we see is not the companion itself, but the regions gravitationally controlled and filled by the wind from the hypergiant. This is a perfect example of the so-called Roche model. This is the first time that such a useful and important model has really been imaged. This hypergiant exemplifies a famous concept!”
Indeed, you can see just such photometric variations as the secondary orbits its host in the VLTI data collected by the AMBER interferometer, backed up by observations from GEMINI’s NICI chronograph:
Looking at the bizarre system of HR 5171. Credit: Olivier Chesneau/ESO/VLT/GEMINI/NICI
The NIGHTFALL program was also used for modeling the eclipsing binary components.
These latest measurements place HR 5171 A firmly in the “Top 10” for largest stars in terms of size known, as well as the largest yellow hypergiant star known This is due mainly to tidal interactions with its companion. Only eight yellow hypergiants have been identified in our Milky Way galaxy. HR 5171 A is also in a crucial transition phase from a red hypergiant to becoming a luminous blue variable or perhaps even a Wolf-Rayet type star, and will eventually end its life as a supernova.
Enormous stars: From left to right, The Pistol Star, Rho Cassiopeiae, Betelgeuse and VY Canis Majoris compared with the orbits of Jupiter (in red) and Neptune (in blue). Remember, HR 5171 A is 50% larger than Betelgeuse! Credit: Anynobody under a Creative Commons Attribution Share-Alike 3.0 Unported license.
HR 5171 A is also known as HD 119796, HIP 67261, and V766 Centauri. Located at Right Ascension 13 Hours 47’ 11” and declination -62 degrees 35’ 23,” HR 5171 culminates just two degrees above the southern horizon at local midnight as seen from Miami in late March.
HR 5171 A: a finder chart. Click to enlarge. Credit: Stellarium
HR 5171 A is a fine binocular object for southern hemisphere observers.
But the good news is, there’s another yellow hypergiant visible for northern hemisphere observers named Rho Cassiopeiae:
The location of Rho Cassiopeiae in the night sky. Credit: Stellarium
Rho Cass is one of the few naked eye examples of a yellow hypergiant star, and varies from magnitude +4.1 to +6.2 over an irregular period.
It’s amusing read the Burnham’s Celestial Handbook entry on Rho Cass. He notes the lack of parallax and the spectral measurements of the day — the early 1960s — as eluding to a massive star with a “true distance… close to 3,000 light years!” Today we know that Rho Cassiopeiae actually lies farther still, at over 8,000 light years distant. Robert Burnham would’ve been impressed even more by the amazing nature of HR 5171 as revealed today by ESO astronomers!
– The AAVSO is always seeking observations from amateur astronomers of variable stars.
The space between the galaxies is expanding. How big is it? Credit: NASA/HST
Did some of the oldest galaxies grow up quickly? That’s an intriguing possibility raised by a research team that found “mature” galaxies some 12 billion light years away, when the universe was less than 2 billion years old.
“Today the universe is old and filled with galaxies that have largely stopped forming stars, a sign of galactic maturity,” stated Caroline Straatman from the Netherlands’ Leiden University, a graduate student who led the research. “However, in the distant past, galaxies were still actively growing by consuming gas and turning it into stars. This means that mature galaxies are expected to be almost non-existent when the universe was still young.”
Using data from the Magellan Baade Telescope’s FourStar Galaxy Evolution Survey and combining with other observatories, researchers looked at the young universe using near infrared wavelengths and found 15 galaxies at an average of 12 billion light-years away. While the galaxies are faint using visual wavelengths, they were easy to spot in infrared — and hosted as many as 100 billion stars per galaxy, on average.
The Milky Way over the ESO 3.6-metre Telescope, a photo submitted via Your ESO Pictures Flickr Group. Credit: ESO/A. Santerne
These galaxies each have a similar mass to the Milky Way, but stopped making stars when the universe was “only 12 percent of its current age”, researchers said. This implies that star-forming happened much more quickly in the past than right now, since the rate is estimated at several hundred times higher than what is observed in the Milky Way now.
It’s not clear what caused the rapid aging, but you can be sure researchers will look into this further. You can read the research in Astrophysical Journal Letters or in preprint version on Arxiv. Other databases used include Hubble’s Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and the Great Observatories Origins Deep Survey.
Multi-wavelength view of the elliptical galaxy NGC 5044. Credit: Digitised Sky Survey/NASA Chandra/Southern Observatory for Astrophysical Research/Very Large Array (Robert Dunn et al. 2010)
Contradicting past theories, cold gas has been found in abundance in some elliptical galaxies — showing that there must be some other explanation why these types of galaxies don’t form new stars. Astronomers believe that the jets from supermassive black holes in these galaxies’ center must push around the gas and prevent stars from forming.
Researchers spotted the gas for the first time using old data from the recently retired Herschel space observatory, which was able to peer well into the infrared — where it spotted carbon ions and oxygen atoms. This find stands against the previous belief that these galaxies were “red and dead”, referring to their physical appearance and the fact that they form no new stars.
“We looked at eight giant elliptical galaxies that nobody had looked at with Herschel before and we were delighted to find that, contrary to previous belief, six out of eight abound with cold gas”, stated Norbert Werner, a researcher at Stanford University in California who led the study.
“These galaxies are red, but with the giant black holes pumping in their hearts, they are definitely not dead,” added Werner.
NGC 1399, an elliptical galaxy about 65 million light years from Earth. Credit: NASA, Chandra
Previously, scientists thought that the galaxies got rid of their cold gas or had used it all up during a burst of earlier star formation. With cold gas found in the majority of the sample, researchers then used other observatories to try to find warmer gas up to tens of millions of Kelvin (or Fahrenheit or Celsius).
X-ray information from NASA’s Chandra X-ray Observatory revealed that there is hot gas cooling in six of the eight galaxies, but not in the remaining two of the sample.
“This is consistent with theoretical expectations: once cooled, the hot gas would become the warm and cold gas that are observed at longer wavelengths. However, in these galaxies the cooling process somehow stopped, and the cold gas failed to condense and form stars,” the European Space Agency stated.
“While the six galaxies with plenty of cold gas harbour moderately active black holes at their centres,” ESA added, “the other two show a marked difference. In the two galaxies without cold gas, the central black holes are accreting matter at frenzied pace, as confirmed by radio observations showing powerful jets of highly energetic particles that stem from their cores.”
This picture was created from images forming part of the Digitized Sky Survey 2. It shows the rich region of sky around the young open star cluster NGC 2547 in the southern constellation of Vela (The Sail). Credit:
ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin
Black holes are big influencers for the early universe; these singularities that were close to ancient stars heated up gas and affected star formation across the cosmos. A new study, however, says that heating happened later than previously thought.
“It was previously believed that the heating occurred very early, but we discovered that this standard picture delicately depends on the precise energy with which the X-rays come out,” stated Rennan Barkana, a co-author of the paper who is an astronomer at Tel Aviv University.
“Taking into account up-to-date observations of nearby black-hole binaries changes the expectations for the history of cosmic heating. It results in a new prediction of an early time (when the universe was only 400 million years old) at which the sky was uniformly filled with radio waves emitted by the hydrogen gas.”
These so-called “black-hole binaries” are star pairs where the larger star exploded into a supernova and left behind a black hole. The strong gravity then yanked gas away from the stellar companion, emitting X-rays in the process. The radiation, as it flows across the universe, is cited as the factor behind gas heating in other parts of space.
