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.”
An artist's conception of a red dwarf solar system. Credit: NASA/JPL-Caltech.
They’re nearby, they’re common and — at least in the latest exoplanet newsflashes hot off the cyber-press — they’re hot. We’re talking about red dwarf stars, those “salt of the galaxy” stars that litter the Milky Way. And while it’s true that there are more of “them” than there are of “us,” not a single one is bright enough to be seen with the naked eye from the skies of Earth.
A reader recently brought up an engaging discussion of what red dwarfs might be within reach of a backyard telescope, and thus this handy compilation was born.
Of course, red dwarfs are big news as possible hosts for life-bearing planets. Though the habitable zones around these stars would be very close in, these miserly stars will shine for trillions of years, giving evolution plenty of opportunity to do its thing. These stars are, however, tempestuous in nature, throwing out potentially planet sterilizing flares.
Red dwarf stars range from about 7.5% the mass of our Sun up to 50%. Our Sun is very nearly equivalent 1000 Jupiters in mass, thus the range of red dwarf stars runs right about from 75 to 500 Jupiter masses.
For this list, we considered red dwarf stars brighter than +10th magnitude, with the single exception of 40 Eridani C as noted.
The closest stars within 14 light years of our solar system. Credit: Wikimedia Commons, Public Domain graphic.
I know what you’re thinking… what about the closest? At magnitude +11, Proxima Centauri in the Alpha Centauri triple star system 4.7 light years distant didn’t quite make the cut. Barnard’s Star (see below) is the closest in this regard. Interestingly, the brown dwarf pair Luhman 16 was discovered just last year at 6.6 light years distant.
Also, do not confuse red dwarfs with massive carbon stars. In fact, red dwarfs actually appear to have more of an orange hue visually! Still, with the wealth of artist’s conceptions (see above) out there, we’re probably stuck with the idea of crimson looking red dwarf stars for some time to come.
Star
Magnitude
Constellation
R.A.
Dec
Groombridge 34
+8/11(v)
Andromeda
00h 18’
+44 01’
40 Eridani C
+11
Eridanus
04h 15’
-07 39’
AX Microscopii/Lacaille 8760
+6.7
Microscopium
21h 17’
-38 52’
Barnard’s Star
+9.5
Ophiuchus
17h 58’
+04 42’
Kapteyn’s Star
+8.9
Pictor
05h 12’
-45 01’
Lalande 21185
+7.5
Ursa Major
11h 03’
+35 58’
Lacaille 9352
+7.3
Piscis Austrinus
23h 06’
-35 51’
Struve 2398
+9.0
Draco
18h 43’
+59 37’
Luyten’s Star
+9.9
Canis Minor
07h 27’
+05 14’
Gliese 687
+9.2
Draco
17h 36’
+68 20’
Gliese 674
+9.9
Ara
17h 29’
-46 54’
Gliese 412
+8.7
Ursa Major
11h 05’
+43 32’
AD Leonis
+9.3
Leo
10h 20’
+19 52’
Gliese 832
+8.7
Grus
21h 34’
-49 01’
Notes on each:
Groombridge 34: Located less than a degree from the +6th magnitude star 26 Andromedae in the general region of the famous galaxy M31, Groombridge 34 was discovered back in 1860 and has a large proper motion of 2.9″ arc seconds per year.
Locating Groombridge 34. Created using Stellarium.
40 Eridani C: Our sole exception to the “10th magnitude or brighter” rule for this list, this multiple system is unique for containing a white dwarf, red dwarf and a main sequence K-type star all within range of a backyard telescope. In sci-fi mythos, 40 Eridani is also the host star for the planet Richese in Dune and the controversial location for Vulcan of Star Trek fame.
Locating 40 Eridani. Created using Stellarium.
AX Microscopii: Also known as Lacaille 8760, AX Microscopii is 12.9 light years distant and is the brightest red dwarf as seen from the Earth at just below naked eye visibility at magnitude +6.7.
A 20 year animation showing the proper motion of Barnard’s Star. Credit: Steve Quirk, images in the Public Domain.
Barnard’s Star: the second closest star system to our solar system next to Alpha Centuari and the closest solitary red dwarf star at six light years distant, Barnard’s Star also exhibits the highest proper motion of any star at 10.3” arc seconds per year. The center of many controversial exoplanet claims in the 20th century, it’s kind of a cosmic irony that in this era of 1790 exoplanets and counting, planets have yet to be discovered around Barnard’s Star!
Kapteyn’s Star: Discovered by Jacobus Kapteyn in 1898, this red dwarf orbits the galaxy in a retrograde motion and is the closest halo star to us at 12.76 light years distant.
Lalande 21185: currently 8.3 light years away, Lalande 21185 will pass 4.65 light years from Earth and be visible to the naked eye in just under 20,000 years.
Lacaille 9352: 10.7 light years distant, this was the first red dwarf star to have its angular diameter measured by the VLT interferometer in 2001.
Struve 2398: A binary flare star system consisting of two +9th magnitude red dwarfs orbiting each other 56 astronomical units apart and 11.5 light years distant.
Luyten’s Star: 12.36 light years distant, this star is only 1.2 light years from the bright star Procyon, which would appear brighter than Venus for any planet orbiting Luyten’s Star.
Gliese 687: 15 light years distant, Gliese 687 is known to have a Neptune-mass planet in a 38 day orbit.
Gliese 674: Located 15 light years distant, ESO’s HARPS spectrograph detected a companion 12 times the mass of Jupiter that is either a high mass exoplanet or a low mass brown dwarf.
Gliese 412: 16 light years distant, this system also contains a +15th magnitude secondary companion 190 Astronomical Units from its primary.
AD Leonis: A variable flare star in the constellation Leo about 16 light years distant.
Gliese 832:Located 16 light years distant, this star is known to have a 0.6x Jupiter mass exoplanet in a 3,416 day orbit.
The closest stars to our solar system over the next 80,000 years. Credit: FrancescoA under a Creative Commons Attribution Share-Alike 3.0 Unported license.
Consider this list a teaser, a telescopic appetizer for a curious class of often overlooked objects. Don’t see you fave on the list? Want to see more on individual objects, or similar lists of quasars, white dwarfs, etc in the range of backyard telescopes in the future? Let us know. And while it’s true that such stars may not have a splashy appearance in the eyepiece, part of the fun comes from knowing what you’re seeing. Some of these stars have a relatively high proper motion, and it would be an interesting challenge for a backyard astrophotographer to build an animation of this over a period of years. Hey, I’m just throwing that out project out there, we’ve got lots more in the files…
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.
A 45-minute time exposure of the southern sky taken in early May shows trailed stars. The fat, bright streak is the planet Mars. Credit: Bob King
A week ago I made a 45-minute time exposure of the southern sky featuring the planet Mars. As the Earth rotated on its axis, the stars trailed across the sky. But take a closer look at the photo and you’ll see something interesting going on.
The trails across the diagonal (upper right to lower left) are straight, those in the top third arc upward or north while those in the bottom third curve downward or south.
I’ve drawn part of the imaginary great circle in the sky called the celestial equator. Residents of cities on or near the Earth’s equator see the celestial equator pass directly overhead. From mid-northern latitudes, it’s about halfway up in the southern sky. From mid-southern latitudes, it’s halfway up in the northern sky. Credit: Bob King
I suspect you know what’s happening here. Mars happens to lie near the celestial equator, an extension of Earth’s equator into the sky. The celestial equator traces a great circle around the celestial sphere much as the equator completely encircles the Earth.
On Earth, cities north of the equator are located in the northern hemisphere, south of the equator in the southern hemisphere. The same is true of the stars. Depending on their location with respect to the celestial equator they belong either to the northern or southern halves of the sky.
Earth’s axis points north to Polaris, the northern hemisphere’s North Star, and south to dim Sigma Octantis. Illustration: Bob King
Next, let’s take a look at Earth’s axis and where each end points. If you live in the northern hemisphere, you know that the axis points north to the North Star or Polaris. As the Earth spins, Polaris appears fixed in the north while all the stars in the northern half of the sky describe a circle around it every 24 hours (one Earth spin). The closer a star is to Polaris, the tighter the circle it describes.
Time exposure centered on Polaris, the North Star. Notice that the closer stars are to Polaris, the smaller the circles they describe. Stars at the edge of the frame make much larger circles. Credit: Bob King
Likewise, from the southern hemisphere, all the southern stars circle about the south pole star, an obscure star named Sigma in the constellation of Octans, a type of navigational instrument. Again, as with Polaris, the closer a star lies to Sigma Octantis, the smaller its circle.
Stars trail around the dim southern pole star Sigma Octantis as seen from the southern hemisphere. The two smudges are the Large and Small Magellanic Clouds, companion galaxies of the Milky Way. Credit: Ted Dobosz
But what about stars on or near the celestial equator? These gems are the maximum distance of 90 degrees from either pole star just as Earth’s equator is 90 degrees from the north and south poles. They “tread the line” between both hemispheres and make circles so wide they appear not as arcs – as the other stars do in the photo – but as straight lines. And that’s why stars appear to be heading in three separate directions in the photograph.
A view of the entire sky as seen from Quito, Ecuador on the equator this evening. The celestial equator crosses directly overhead while each pole star lies 90 degrees away on opposite horizons. Stellarium
In so many ways, we see aspects of our own planet in the stars above.
The supernova remnant G352.7-0.1 in a composite image with X-rays from the Chandra X-Ray Telescope (blue), radio waves from the Very Large Array (pink), infrared information from the Spitzer Space Telescope (orange) and optical data from the Digital Sky Survey (white). Credit: X-ray: NASA/CXC/Morehead State Univ/T.Pannuti et al.; Optical: DSS; Infrared: NASA/JPL-Caltech; Radio: NRAO/VLA/Argentinian Institute of Radioastronomy/G.Dubner
Shining 24,000 light-years from Earth is an expanding leftover of a supernova that is doing a great cleanup job in its neighborhood. As this new composite image from NASA reveals, G352.7-0.1 (G352 for short) is more efficient than expected, picking up debris equivalent to about 45 times the mass of the Sun.
“A recent study suggests that, surprisingly, the X-ray emission in G352 is dominated by the hotter (about 30 million degrees Celsius) debris from the explosion, rather than cooler (about 2 million degrees) emission from surrounding material that has been swept up by the expanding shock wave,” the Chandra X-Ray Observatory’s website stated.
“This is curious because astronomers estimate that G352 exploded about 2,200 years ago, and supernova remnants of this age usually produce X-rays that are dominated by swept-up material. Scientists are still trying to come up with an explanation for this behavior.”
The difference between a neutron star and a quark star (Chandra)
You may have heard that CERN announced the discovery (confirmation, actually. See addendum below.) of a strange particle known as Z(4430). A paper summarizing the results has been published on the physics arxiv, which is a repository for preprint (not yet peer reviewed) physics papers. The new particle is about 4 times more massive than a proton, has a negative charge, and appears to be a theoretical particle known as a tetraquark. The results are still young, but if this discovery holds up it could have implications for our understanding of neutron stars.
A periodic table of elementary particles. Credit: Wikipedia
The building blocks of matter are made of leptons (such as the electron and neutrinos) and quarks (which make up protons, neutrons, and other particles). Quarks are very different from other particles in that they have an electric charge that is 1/3 or 2/3 that of the electron and proton. They also possess a different kind of “charge” known as color. Just as electric charges interact through an electromagnetic force, color charges interact through the strong nuclear force. It is the color charge of quarks that works to hold the nuclei of atoms together. Color charge is much more complex than electric charge. With electric charge there is simply positive (+) and its opposite, negative (-). With color, there are three types (red, green, and blue) and their opposites (anti-red, anti-green, and anti-blue).
Because of the way the strong force works, we can never observe a free quark. The strong force requires that quarks always group together to form a particle that is color neutral. For example, a proton consists of three quarks (two up and one down), where each quark is a different color. With visible light, adding red, green and blue light gives you white light, which is colorless. In the same way, combining a red, green and blue quark gives you a particle which is color neutral. This similarity to the color properties of light is why quark charge is named after colors.
Combining a quark of each color into groups of three is one way to create a color neutral particle, and these are known as baryons. Protons and neutrons are the most common baryons. Another way to combine quarks is to pair a quark of a particular color with a quark of its anti-color. For example, a green quark and an anti-green quark could combine to form a color neutral particle. These two-quark particles are known as mesons, and were first discovered in 1947. For example, the positively charged pion consists of an up quark and an antiparticle down quark.
Under the rules of the strong force, there are other ways quarks could combine to form a neutral particle. One of these, the tetraquark, combines four quarks, where two particles have a particular color and the other two have the corresponding anti-colors. Others, such as the pentaquark (3 colors + a color anti-color pair) and the hexaquark (3 colors + 3 anti-colors) have been proposed. But so far all of these have been hypothetical. While such particles would be color neutral, it is also possible that they aren’t stable and would simply decay into baryons and mesons.
There has been some experimental hints of tetraquarks, but this latest result is the strongest evidence of 4 quarks forming a color neutral particle. This means that quarks can combine in much more complex ways than we originally expected, and this has implications for the internal structure of neutron stars.
Very simply, the traditional model of a neutron star is that it is made of neutrons. Neutrons consist of three quarks (two down and one up), but it is generally thought that particle interactions within a neutron star are interactions between neutrons. With the existence of tetraquarks, it is possible for neutrons within the core to interact strongly enough to create tetraquarks. This could even lead to the production of pentaquarks and hexaquarks, or even that quarks could interact individually without being bound into color neutral particles. This would produce a hypothetical object known as a quark star.
This is all hypothetical at this point, but verified evidence of tetraquarks will force astrophysicists to reexamine some the assumptions we have about the interiors of neutron stars.
Addendum: It has been pointed out that CERN’s results are not an original discovery, but rather a confirmation of earlier results by the Belle Collaboration. The Belle results can be found in a 2008 paper in Physical Review Letters, as well as a 2013 paper in Physical Review D. So credit where credit is due.
The Milky Way, The Large and Small Magellanic Clouds, Zodiacal Light, and Venus as seen from the Karoo Desert in South Africa early this month. Credit: Cory Schmitz.
Have you been following the planet Venus this season? 2014 sees the brightest planet in our Earthly skies spend a majority of its time in the dawn. Shining at magnitude -3.8, it’s hard to miss in the morning twilight. But dazzling Venus is visiting two unique celestial objects over the next week, and both present unique observing challenges for the seasoned observer.
First up is an interesting close conjunction of the planets Venus and Neptune on the morning of Saturday, April 12th. Closest conjunction occurs at 3:00 Universal Time (UT) April 12th favoring Eastern Europe, the Middle East and eastern Africa, when the two worlds appear to be just 40 arc minutes apart, a little over – by about 10’ – the apparent size of a full Moon. Shining at magnitude +7.8 and 30,000 times fainter than Venus, you’ll need a telescope to tease out Neptune from the pre-dawn sky. Both objects will, however, easily fit in a one degree field of view, in addition to a scattering of other stars.
Looking to the east the morning of April 12th from the U.S. East Coast near latitude 30 degrees north. Nearby stars are annotated in red by magnitude with decimals omitted. Created using Stellarium, click to enlarge.
At low power, Venus will display a 59% illuminated gibbous phase 20” across on the morning of the 12th, while Neptune will show a tiny disk barely 2” across. Still, this represents the first chance for viewers to recover Neptune since solar conjunction behind the Sun on February 23rd, 2014, using dazzling Venus as a guide.
Both sit 45 degrees west of the Sun and currently rise around 3 to 4 AM local dependent on latitude.
This is one of the closest planet-planet conjunctions for 2014. The closest is Venus and Jupiter at just 0.2 degrees apart on August 18th. This will represent the brightest planet versus planet conjunction for the year, and is sure to illicit multiple “what’s those two bright stars in the sky?” queries from morning commuters… hopefully, such sightings won’t result in any border skirmishes worldwide.
Now, for the mandatory Wow factor. On the date of conjunction, Earth-sized Venus is 0.84 Astronomical Units (A.U.s) or over 130 million kilometres distant. Ice giant Neptune, however, is 30.7 AUs or 36 times as distant, and only appears tiny though it’s almost four times larger in diameter. Sunlight reflected from Venus takes 7 minutes to reach Earth, but over four hours to arrive from Neptune. We’ve visited Venus lots, and the Russians have even landed there and returned images from its smoldering surface, but we’ve only visited Neptune once, during a brief flyby of Voyager 2 in 1989.
From Neptune looking back on April 12th, Earth and Venus would appear less than 1 arc minute apart…. though they’d also be just over one degree from the Sun!
The “shadow path” of the occultation of Lambda Aquarii by Venus on April 16th. Credit: IOTA/Steve Preston/www.asteroidoccultation/Occult 4.0.
But an even more bizarre event happens a few days later on April 16th, though only a small region of the world in the South Pacific may bare witness to it.
Next Wednesday from 17:59 to 18:13 UT Venus occults the +3.7 magnitude star HIP 112961 also known as Lambda Aquarii on the morning of April 16th 2014.
Venus will be a 61% illuminated gibbous phase 19” in diameter. Unfortunately, although North America is rotated towards the event, it’s also in the middle of the day.
The best prospects to observe the occultation are from New Zealand and western Pacific at dawn. The star will disappear behind the bright limb of Venus in dawn twilight before emerging on its dark limb 5 minutes later as seen from New Zealand.
The path of Lambda Aquarii behind Venus as seen from New Zealand the morning of the 16th. Created in Starry Night.
Note: New Zealand switched back to standard time on April 6th – it’s currently Fall down under – and local sunrise occurs around ~7:40 AM.
Lambda Aquarii is a 3.6 solar mass star located 390 light years distant. As far as we know, it’s a solitary star, though there’s always a chance that a companion could make itself known as it emerges on the dark limb of Venus. Such an observation will, however, be extremely difficult, as Venus is still over 700 times brighter than the star!
North Americans get to see the pair only 20’ apart on the morning of the 12th.
One degree fields of view worldwide showing Venus and Lambda Aquarii at 7AM local. Credit: Starry Night.
And further occultation adventures await Venus in the 21st century. On October 1st, 2044 it will occult Regulus… and on November 22nd, 2065 it will actually occult Jupiter!
Such pairings give us a chance to image Venus with a “pseudo-moon.” Early telescopic observers made numerous sightings of a supposed Moon of Venus, and the hypothetical object even merited the name Neith for a brief time. Such sightings were most likely spurious internal reflections due to poor optics or nearby stars, but its fun to wonder what those observers of old might’ve seen.
… and speaking of moons, don’t miss a chance to see Venus near the daytime Moon April 25th. Follow us as @Astroguyz on Twitter as we give shout outs to these and other strange pairings daily!
Artist's conception of how the Baryon Oscillation Spectroscopic Survey uses quasars to make measurements. The light these objects sends out gets absorbed by gas in between the receiver and the source. The gas is then "imprinted wiht a subtle ring-like pattern of known physical scale", the Sloan Digital Sky Survey stated. Credit: Zosia Rostomian (Lawrence Berkeley National Laboratory) and Andreu Font-Ribera (BOSS Lyman-alpha team, Berkeley Lab.)
For those who saw the Cosmos episode on William Herschel describing telescopes as time machines, here is a clear example of that. By examining 140,000 objects called quasars (galaxies with an active black hole at their centers), astronomers have charted the expansion rate of the universe — not now, but 10.8 billion years ago.
This is the most precise measurement ever of the universe’s expansion rate at any point in time, the science teams said, with the calculation showing the universe was expanding by 1% every 44 million years at that time. (That figure is to 2% precision, the researchers added.)
“If we look back to the Universe when galaxies were three times closer together than they are today, we’d see that a pair of galaxies separated by a million light-years would be drifting apart at a speed of 68 kilometers per second as the Universe expands,” stated Andreu Font-Ribera of the Lawrence Berkeley National Laboratory, who led one of the two analyses.
The researchers used a telescope called the Sloan Digital Sky Survey, a 2.5-meter telescope at Apache Point Observatory in New Mexico. The discovery was made during Sloan’s Baryon Oscillation Spectroscopic Survey, or BOSS, whose aim has been to figure out the expansion and acceleration of the universe.
The accelerating, expanding Universe. Credit: NASA/WMAP
“BOSS determines the expansion rate at a given time in the Universe by measuring the size of baryon acoustic oscillations (BAO), a signature imprinted in the way matter is distributed, resulting from sound waves in the early Universe,” the Sloan Digital Sky Survey stated. “This imprint is visible in the distribution of galaxies, quasars, and intergalactic hydrogen throughout the cosmos.”
Font-Ribera and his collaborators examined how quasars are distributed compared to hydrogen gas to calculate distance. The other analysis, led by Timothée Delubac (Centre de Saclay, France), examined the hydrogen gas to see patterns and measure mass distribution.
You can read more about Font-Ribera’s team’s research in preprint version on Arxiv. Delubac’s research does not appear to be available online, but the title is “Baryon Acoustic Oscillations in the Ly-alpha forest of BOSS DR11 quasars” and it has been submitted to Astronomy & Astrophysics.
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.
