Posted on by Shannon Hall

Mapping Dark Matter 4.5 Billion Light-years Away

This image shows the galaxy MCS J0416.1–2403, one of six clusters targeted by the Hubble Frontier Fields programme. The blue in this image is a mass map created by using new Hubble observations combined with the magnifying power of a process known as gravitational lensing. In red is the hot gas detected by NASA’s Chandra X-Ray Observatory and shows the location of the gas, dust and stars in the cluster. The matter shown in blue that is separate from the red areas detected by Chandra consists of what is known as dark matter, and which can only be detected directly by gravitational lensing.Credit: ESA/Hubble, NASA, HST Frontier Fields. Acknowledgement: Mathilde Jauzac (Durham University, UK) and Jean-Paul Kneib (École Polytechnique Fédérale de Lausanne, Switzerland).

The Milky Way measures 100 to 120 thousand light-years across, a distance that defies imagination. But clusters of galaxies, which comprise hundreds to thousands of galaxies swarming under a collective gravitational pull, can span tens of millions of light-years.

These massive clusters are a complex interplay between colliding galaxies and dark matter. They seem impossible to map precisely. But now an international team of astronomers using the NASA/ESA Hubble Space Telescope has done exactly this — precisely mapping a galaxy cluster, dubbed MCS J0416.1–2403, 4.5 billion light-years away.

“Although we’ve known how to map the mass of a cluster using strong lensing for more than twenty years, it’s taken a long time to get telescopes that can make sufficiently deep and sharp observations, and for our models to become sophisticated enough for us to map, in such unprecedented detail, a system as complicated as MCS J0416.1–2403,” said coauthor Jean-Paul Kneib in a press release.

Measuring the amount and distribution of mass within distant objects can be extremely difficult. Especially when three quarters of all matter in the Universe is dark matter, which cannot be seen directly as it does not emit or reflect any light. It interacts only by gravity.

But luckily large clumps of matter warp and distort the fabric of space-time around them. Acting like lenses, they appear to magnify and bend light that travels past them from more distant objects.

This effect, known as gravitational lensing, is only visible in rare cases and can only be spotted by the largest telescopes. Even galaxy clusters, despite their massive size, produce minimal gravitational effects on their surroundings. For the most part they cause weak lensing, making even more distant sources appear as only slightly more elliptical across the sky.

However, when the alignment of the cluster and distant object is just right, the effects can be substantial. The background galaxies can be both brightened and transformed into rings and arcs of light, appearing several times in the same image. It is this effect, known as strong lensing, which helped astronomers map the mass distribution in MCS J0416.1–2403.

“The depth of the data lets us see very faint objects and has allowed us to identify more strongly lensed galaxies than ever before,” said lead author Dr Jauzac. “Even though strong lensing magnifies the background galaxies they are still very far away and very faint. The depth of these data means that we can identify incredibly distant background galaxies. We now know of more than four times as many strongly lensed galaxies in the cluster than we did before.”

Using Hubble’s Advanced Camera for Surveys, the astronomers identified 51 new multiply imaged galaxies around the cluster, quadrupling the number found in previous surveys. This effect has allowed Jauzac and her colleagues to calculate the distribution of visible and dark matter in the cluster and produce a highly constrained map of its mass.

The total mass within the cluster is 160 trillion times the mass of the Sun, with an uncertainty of 0.5%. It’s the most precise map ever produced.

But Jauzac and colleagues don’t plan on stopping here. An even more accurate picture of the galaxy cluster will have to include measurements from weak lensing as well. So the team will continue to study the cluster using ultra-deep Hubble imaging.

They will also use ground-based observatories to measure any shifts in galaxies’ spectra and therefore note the velocities of the contents of the cluster. Combining all measurements will not only further enhance the detail, but also provide a 3D model of the galaxies within the cluster, shedding light on its history and evolution.

This work has been accepted for publication in the Monthly Notices of the Royal Astronomy and is available online.

Posted on by Shannon Hall

ESO’s La Silla Observatory Reveals Beautiful Star Cluster “Laboratory”

In this image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile young stars huddle together against a backdrop of clouds of glowing gas and lanes of dust. The star cluster, known as NGC 3293, would have been just a cloud of gas and dust itself about ten million years ago, but as stars began to form it became the bright group we see here. Clusters like this are celestial laboratories that allow astronomers to learn more about how stars evolve. Credit: ESO/G. Beccari

Any human being knows the awe-inspiring wonder of a splash of stars against a dark backdrop. But it takes a skilled someone to truly appreciate a distant object viewed through an eyepiece. Your gut tightens as you realize that the tiny fuzzy blob is really thousands of light-years away.

That wave of amazement is encouraged by understanding and knowledge.

Stunning photographs of the cosmos further convey the beauty that arises from the simple interplay of dust, light and gas on absolutely massive and distant scales. The striking image above from ESO’s La Silla Observatory in Chile is but one example.

Stars are born in enormous clouds of gas and dust. Small pockets in these clouds collapse under the pull of gravity, eventually becoming so hot that they ignite nuclear fusion. The result is a cluster of tens to hundreds of thousands of stars bound together by their mutual gravitational attraction.

Every star in a cluster is roughly the same age and has the same chemical composition. They’re the closest thing astronomers have to a controlled laboratory environment.

This chart shows the location of the bright open star cluster NGC 3293 in the southern constellation of Carina (The Keel). All the stars visible to the naked eye on a clear and dark night are marked, along with the positions of some nebulae and clusters. The location of NGC 3293 is marked with a red circle. This cluster is bright enough to be seen without optical aid in good conditions and is a spectacular sight in a moderate-sized telescope. Credit: ESO, IAU and Sky & Telescope
This chart shows the location of the bright open star cluster NGC 3293 (marked by a red circle) in the southern constellation of Carina. Image Credit: ESO / IAU / Sky & Telescope

The star cluster, NGC 3293, is located 8000 light-years from Earth in the constellation of Carina. It was first spotted by the French astronomer Nicolas-Louis de Lacaille during his stay in South Africa in 1751. Because it stands as one of the brightest clusters in the southern sky, de Lacaille was able to site it in a tiny telescope with an aperture of just 12 millimeters.

The cluster is less than 10 million years old, as can be seen by the abundance of hot, blue stars. Despite some evidence suggesting that there is still some ongoing star formation, it is thought that most, if not all, of the nearly 50 stars were born in one single event.

But even though these stars are all the same age, they do not all have the dazzling appearance of stars in their infancy. Some look positively elderly. The reason is simple: stars of different size, evolve at different speeds. More massive stars speed through their evolution, dying quickly, while less massive stars can live tens of billions of years.

Take the bright orange star at the bottom right of the cluster. Stars initially draw their energy from burning hydrogen into helium deep within their cores. But this star ran out of hydrogen fuel faster than its neighbors, and quickly evolved into a cool and bright, giant star with a contracted core but an extended atmosphere.

It’s now a cool, red giant, in a new stage of evolution, while its neighbors remain hot, young stars.

Eventually the star will collapse under its own gravity, throwing off its outer layers in a supernova explosion, and leaving behind a neutron star or a black hole. The peppering shock waves will likely initiate further star formation in the ever-changing laboratory.

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Source: ESO

Posted on by Shannon Hall

First Exoplanet Discovered Beyond the “Snow Line”

This artist's conception shows the Uranus-sized exoplanet Kepler-421b, which orbits an orange, type K star about 1,000 light-years from Earth. Kepler-421b is the transiting exoplanet with the longest known year, circling its star once every 704 days. It is located beyond the "snow line" – the dividing line between rocky and gaseous planets – and might have formed in place rather than migrating from a different orbit. David A. Aguilar (CfA)

Data from NASA’s crippled Kepler space telescope has unleashed a windfall of hot Jupiters — sizzling gas giants that circle their host star within days — and only a handful of Earth-like planets. A quick analysis might make it seem as though hot Jupiters are far more common than their smaller and more distant counterparts.

But in large surveys, astronomers have to be careful of the observational biases introduced into their data. Kepler, for example, mainly finds broiling furnace worlds close to their host stars. These are easier to spot than small exoplanets that take hundreds of days to transit.

New data, however, shows a transiting exoplanet, Kepler-421b, with the longest known year, clocking in at 704 days.

“Finding Kepler-421b was a stroke of luck,” said lead author David Kipping from the Harvard-Smithsonian Center for Astrophysics in a press release. “The farther a planet is from its star, the less likely it is to transit the star from Earth’s point of view. It has to line up just right.”

Kepler-416b's folded light curve. Image Credit:
Kepler-421b’s folded light curve. Blue points are data from the first transit observed, and red points are the second transit.  Image Credit: Kipping et al.

Kepler-421b is roughly 4 times Earth’s girth and at least 60 times Earth’s mass. It circles its host star at about 1.2 times the distance from the Earth to the Sun. But because its host star is much smaller than our Sun, this places its orbit beyond the snow line — the dividing line between rocky and gas planets.

On Earth, snow lines typically form at high elevations where falling temperatures turn atmospheric moisture to snow. Similarly, in planetary systems, snow lines are thought to form in the distant, colder reaches of the stars’ disk.

Depending on the distance from the star, however, other more exotic molecules — such as carbon dioxide, methane, and carbon monoxide — can freeze and turn to snow. This forms a frost on dust grains: the building blocks of planets and comets.

“The snow line is a crucial distance in planet formation theory. We think all gas giants must have formed beyond this distance,” said Kipping.

The fact that this gas giant is still beyond this distance, roughly 4 billion years after formation, suggests that it’s the first non-migrating gas giant in a transiting system found.

Astronomers currently think gas giants form by small rocky cores that glom together until the body is massive enough to accrete a gaseous envelope. As they grow, they migrate inward, sometimes moving as close to their host star as Mercury is to the Sun.

Kepler-421b may be the first exoplanet discovered to have formed in situ. But further observations, especially those of its atmosphere, will help shed light on its formation history. Unfortunately given its long year, it won’t transit again until February, 2016.

The research has been accepted for publication in The Astrophysical Journal and is available online.

Posted on by Shannon Hall

Distant Stellar Atmospheres Shed Light on How Jupiter-like Planets Form

Interior of Jupiter. Image Credit: NASA / R. J. Hall

It’s likely that Jupiter-like planets’ origins root back to either the rapid collapse of a dense cloud or small rocky cores that glom together until the body is massive enough to accrete a gaseous envelope.

Although these two competing theories are both viable, astronomers have, for the first time, seen the latter “core accretion” theory in action. By studying the exoplanet’s host star they’ve shed light on the composition of the planet’s rocky core.

“Our results show that the formation of giant planets, as well as terrestrial planets like our own Earth, leaves subtle signatures in stellar atmospheres”, said lead author and PhD student Marcelo Tucci Maia from University of São Paulo, Brazil, in a press release.

Maia and colleagues pointed the 3.5-meter Canada-France-Hawaii Telescope toward the constellation Cygnus, in order to take a closer look at two Sun-like stars in the distant 16 Cyg triple-star system. Both stars, having formed together from the same gaseous disk over 10 billion years ago and having reached the same mass, are nearly solar twins.

But only one star, 16 Cygni B, hosts a giant planet. By decomposing the light from the two stars into their wavelengths and looking at the difference between the two stars, the team was able to detect signatures left from the planet formation process on 16 Cygni B.

It’s the perfect laboratory to study the formation of giant planets.

Difference in chemical composition between the stars 16 Cyg A and 16 Cyg B, versus the condensation temperature of the elements in the proto-planetary nebula. If the stars had identical chemical compositions then the difference (A-B) would be zero. The star 16 Cyg A is richer in all elements relative to star 16 Cyg B. In other words, star 16 Cyg B, the host star of a giant planet, is deficient in all chemical elements, especially in the refractory elements (those with high condensation temperatures and that form dust grains more easily), suggesting evidence of a rocky core in the giant planet 16 Cyg Bb. Credits: M. Tucci Maia, J. Meléndez, I. Ramírez.
Difference in chemical composition between the stars 16 Cyg A and 16 Cyg B, versus the condensation temperature of the elements in the proto-planetary nebula. Image Credit: M. Tucci Maia, J. Meléndez, I. Ramírez.

Maia and colleagues found that the star 16 Cygni A is enhanced in all chemical elements relative to 16 Cygni B. Hence, the metals removed from 16 Cygni B were most likely removed from the protoplanetary disk in order to form the planet.

On top of the overall deficiency in all elements, 16 Cygni B has an added deficiency in the refractory elements — those with high condensation temperatures that form dust grains more easily — such as iron, aluminum, nickel, magnesium, scandium, and silicon. This helps verify what astronomers have expected all along: rocky cores are rich in refractory elements.

The team was able to decipher that these missing elements likely created a rocky core with a mass of about 1.5 to 6 Earth masses, which is similar to the estimate of Jupiter’s core.

“16 Cyg is a remarkable system, but certainly not unique,” said coauthor Ivan Ramírez from the University of Texas. “It is special because it is nearby; however, there are many other binary stars with twin components on which this experiment could be performed. This could help us find planet-host stars in binaries in a much more straightforward manner compared to all other planet-finding techniques we have available today.”

The results were accepted for publication in The Astrophysical Journal Letters and are available online.

Posted on by Shannon Hall

New VLT Observations Clear Up Dusty Mystery

The dwarf galaxy UGC 5189A, site of the supernova SN 2010jl. Image Credit: ESO

The Universe is overflowing with cosmic dust. Planets form in swirling clouds of dust around a young star; Dust lanes hide more-distant stars in the Milky Way above us; And molecular hydrogen forms on the dust grains in interstellar space.

Even the soot from a candle is very similar to cosmic carbon dust. Both consist of silicate and amorphous carbon grains, although the size grains in the soot are 10 or more times bigger than typical grain sizes in space.

But where does the cosmic dust come from?

A group of astronomers has been able to follow cosmic dust being created in the aftermath of a supernova explosion. The new research not only shows that dust grains form in these massive explosions, but that they can also survive the subsequent shockwaves.

Stars initially draw their energy by fusing hydrogen into helium deep within their cores. But eventually a star will run out of fuel. After slightly messy physics, the star’s contracted core will begin to fuse helium into carbon, while a shell above the core continues to fuse hydrogen into helium.

The pattern continues for medium to high mass stars, creating layers of different nuclear burning around the star’s core. So the cycle of star birth and death has steadily produced and dispersed more heavy elements throughout cosmic history, providing the substances necessary for cosmic dust.

“The problem has been that even though dust grains composed of heavy elements would form in supernovae, the supernova explosion is so violent that the grains of dust may not survive,” said coauthor Jens Hjorth, head of the Dark Cosmology Center at the Niels Bohr Institute in a press release. “But cosmic grains of significant size do exist, so the mystery has been how they are formed and have survived the subsequent shockwaves.”

The team led by Christa Gall used ESO’s Very Large Telescope at the Paranal Observatory in northern Chile to observe a supernova, dubbed SN2010jl, nine times in the months following the explosion, and for a tenth time 2.5 years after the explosion. They observed the supernova in both visible and near-infrared wavelengths.

SN2010jl was 10 times brighter than the average supernova, making the exploding star 40 times the mass of the Sun.

“By combining the data from the nine early sets of observations we were able to make the first direct measurements of how the dust around a supernova absorbs the different colours of light,” said lead author Christa Gall from Aarhus University. “This allowed us to find out more about the dust than had been possible before.”

The results indicate that dust formation starts soon after the explosion and continues over a long time period.

The dust initially forms in material that the star expelled into space even before it exploded. Then a second wave of dust formation occurs, involving ejected material from the supernova. Here the dust grains are massive — one thousandth of a millimeter in diameter — making them resilient to any following shockwaves.

“When the star explodes, the shockwave hits the dense gas cloud like a brick wall. It is all in gas form and incredibly hot, but when the eruption hits the ‘wall’ the gas gets compressed and cools down to about 2,000 degrees,” said Gall. “At this temperature and density elements can nucleate and form solid particles. We measured dust grains as large as around one micron (a thousandth of a millimeter), which is large for cosmic dust grains. They are so large that they can survive their onward journey out into the galaxy.”

If the dust production in SN2010jl continues to follow the observed trend, by 25 years after the supernova explosion, the total mass of dust will have half the mass of the Sun.

The results have been published in Nature and are available for download here. Niels Bohr Institute’s press release and ESO’s press release are also available.

Posted on by Shannon Hall

‘Gyrochronology’ Allows Astronomers to Find True Sun-like Stars

Credit: NASA/European Space Agency

There’s no doubt the term “Earth-like” is a bit of a misnomer. It requires only that a planet is both Earth-size (less than 1.25 times Earth’s girth and less than twice Earth’s mass) and circles its host star within the habitable zone.

But defining a “Sun-like” star may be just as difficult. A solar twin should have a temperature, mass, age, radius, metallicity, and spectral type similar to the Sun. Although measuring most of these factors isn’t easy, aging a star is extremely difficult, and astronomers tend to ignore it when concluding if a star is Sun-like or not.

This is less than ideal, given that our Sun and all stars change over time. Thankfully a technique — gyrochronology — is allowing astronomers to measure stellar ages based only on spin and find true solar analogues.

“We have found stars with properties that are close enough to those of the Sun that we can call them ‘solar twins,'” said lead author Jose Dias do Nascimento from the Harvard-Smithsonian Center for Astrophysics (CfA) in a press release.

do Nascimento and colleagues measured the spin of 75 stars by looking for changes in brightness caused by dark star spots, rotating in and out of view. Although this difference is minute, clocking in at a few percent or less, NASA’s Kepler spacecraft excels at extracting such small changes in brightness.

On average, the sampled stars spin once every 19 days, compared to the 25-day rotation period of the Sun. This makes most of the stars slightly younger than the Sun, as younger stars spin faster than older ones.

The relationship between stellar spin and age was determined in previous research by Soren Meibom (CfA) and colleagues, who measured the rotation rates for stars in a one-billion-year-old cluster. Since the stars already had a known age, the team could measure their spin rates and calibrate the previous relationship.

Using this method, do Nascimento and colleagues found 22 true solar analogues within their data set of 75 stars.

“With solar twins we can study the past, present, and future of stars like our Sun,” said do Nascimento. “Consequently, we can predict how planetary systems like our solar system will be affected by the evolution of their central stars.”

The results were accepted for publication in The Astrophysical Journal Letters and are available online.

Posted on by Shannon Hall

NameExoWorlds, an IAU Worldwide Contest to Name Alien Planets, Continues Controversy

This artist’s view shows an extrasolar planet orbiting a star (the white spot in the right).
This artist’s view shows an extrasolar planet orbiting a star (the white spot in the right). Image Credit: IAU/M. Kornmesser/N. Risinger (skysurvey.org)

The International Astronomical Union has unveiled a worldwide contest, NameExoWorlds, which gives the public a role in naming planets and their host stars beyond the solar system.

It’s the latest chapter in a years-long controversy over how celestial objects, including exoplanets, are classified and named.

Although the IAU has presided over the long process of naming astronomical objects for nearly a century, until last year they didn’t feel the need to include exoplanets on this long list.

As late as March 2013, the IAU’s official word on naming exoplanets was: “The IAU sees no need and has no plan to assign names to these objects at the present stage of our knowledge.” Since there was seemingly going to be so many exoplanets, the IAU saw it too difficult to name them all.

Other organizations, however, such as the SETI institute and the space company Uwingu leapt at the opportunity to engage the public in providing names for exoplanets. Their endeavors have been widely popular with the general public, but generated discussion about how ‘official’ the names would be.

The IAU issued a later statement in April 2014 (which Universe Today covered with vigor) and claimed that these two campaigns had no bearing on the official naming process. By August 2014, the IAU had introduced new rules for naming exoplanets, drastically changing their stance and surprising many.

Now in partnership with Zooniverse, a citizen-science organization, the IAU has drawn up a list of 305 well-characterized exoplanets in 206 solar systems. Starting in September, astronomy organizations can register for the opportunity to select planets for naming.

In October, the IAU plans to ask the registered organizations to vote for the 20 to 30 worlds on the list that they want to name. The exact number will depend on the number of registered groups. In December, those groups can propose names for the worlds that get the most votes. Groups can only propose names in accordance with the following set of rules. A name must be:

—   16 characters or less in length

—   Preferably one word

—   Pronounceable (in some language)

—   Non-offensive

—   Not too similar to an existing name of an astronomical object

Starting in March 2015, the list of proposed names will be put up to an Internet vote. The winners will be validated by the IAU, and announced during a ceremony at the IAU General Assembly in Honolulu in August 2015.

The popular name for a given exoplanet won’t replace the scientific name. But it will carry the IAU seal of approval.

Astronomer Alan Stern, principal investigator of the New Horizons mission to Pluto and CEO of Uwingu told Universe Today’s Senior Editor, Nancy Atkinson, that he was not surprised by the IAU’s new statement. “To my eye though, it’s just more IAU elitism, they can’t seem to get out of their elitist rut thinking they own the Universe.”

“Uwingu’s model is in our view far superior — people can directly name planets around other stars, with no one having to approve the choices,” Stern continued. “With 100 billion plus planets in the galaxy, why bother with committees of elites telling people what they do and don’t approve of?”

If nothing else, the controversy has sparked multiple venues to name exoplanets and more importantly learn about these alien worlds.

Posted on by Shannon Hall

Supermassive Black Hole Blasting Molecular Hydrogen Solves Outstanding Mystery

An artist's conception of a supermassive black hole's jets. Credit: NASA / Dana Berry / SkyWorks Digital
An artist's conception of a supermassive black hole's jets. Credit: NASA / Dana Berry / SkyWorks Digital

The supermassive black holes in the cores of most massive galaxies wreak havoc on their immediate surroundings. During their most active phases — when they ignite as luminous quasars — they launch extremely powerful and high-velocity outflows of gas.

These outflows can sweep up and heat material, playing a pivotal role in the formation and evolution of massive galaxies. Not only have astronomers observed them across the visible Universe, they also play a key ingredient in theoretical models.

But the physical nature of the outflows themselves has been a longstanding mystery. What physical mechanism causes gas to reach such high speeds, and in some cases be expelled from the galaxy?

A new study provides the first direct evidence that these outflows are accelerated by energetic jets produced by the supermassive black hole.

Using the Very Large Telescope in Chile, a team of astronomers led by Clive Tadhunter from Sheffield University, observed the nearby active galaxy IC 5063. At locations in the galaxy where its jets are impacting regions of dense gas, the gas is moving at extraordinary speeds of over 600,000 miles per hour.

“Much of the gas in the outflows is in the form of molecular hydrogen, which is fragile in the sense that it is destroyed at relatively low energies,” said Tadhunter in a press release. “I find it extraordinary that the molecular gas can survive being accelerated by jets of highly energetic particles moving at close to the speed of light.

As the jets travel through the galactic matter, they disrupt the surrounding gas and generate shock waves. These shock waves not only accelerate the gas, but also heat it. The team estimates the shock waves heat the gas to temperatures high enough to ionize the gas and dissociate the molecules. Molecular hydrogen is only formed in the significantly cooler post-shock gas.

“We suspected that the molecules must have been able to reform after the gas had been completely upset by the interaction with a fast plasma jet,” said Raffaella Morganti from the Kapteyn Institute Groningen University. “Our direct observations of the phenomenon have confirmed that this extreme situation can indeed occur. Now we need to work at describing the exact physics of the interaction.”

In interstellar space, molecular hydrogen forms on the surface of dust grains. But in this scenario, the dust is likely to have been destroyed in the intense shock waves. While it is possible for molecular hydrogen to form without the aid of dust grains (as seen in the early Universe) the exact mechanism in this case is still unknown.

The research helps answer a longstanding question — providing the first direct evidence that jets accelerate the molecular outflows seen in active galaxies — and asks new ones.

The results were published in Nature and are available online.

Posted on by Shannon Hall

Missing Light Crisis: The Universe Seems a Little Too Dark

The Milky Way as seen from Devil's Tower, Wyoming. Image Credit: Wally Pacholka

There are few moments more breathtaking than standing beneath a brilliant starry sky. Thousands of small specks of light mark only the beginning of the vast cosmic arena, with its unimaginable vistas of time and space. The Milky Way, wrapping above in a cosmic sheet of colors and patterns, also hints that there’s more than meets the eye.

Most of us long for these dark nights, far away from the city lights. But a new study suggests the Universe is a little too dark.

The vast reaches of empty space are bridged by filaments of hydrogen and helium. But there’s a disconnect between how bright the large-scale structure of the Universe is expected to be and how bright it actually is.

In a recent study, a team of astronomers led by Juna Kollmeier from the Carnegie Institute for Science found the light from known populations of stars and quasars is not nearly enough to explain observations of intergalactic hydrogen.

In a brightly lit Universe, intergalactic hydrogen will be easily destroyed by energetic photons, meaning images of the large-scale structure will actually appear dimmer. Whereas in a dim Universe, there are fewer photons to destroy the intergalactic hydrogen and images will appear brighter.

Hubble Space Telescope observations of the large-scale structure show a brightly lit Universe. But supercomputer simulations using only the known sources of ultraviolet light produces a dimly lit Universe. The difference is a stunning 400 percent.

Computer simulations of intergalactic hydrogen in a "dimly lit" universe (left) and a "brightly lit" universe (right) that has five times more of the energetic photons that destroy neutral hydrogen atoms. Hubble Space Telescope observations of hydrogen absorption match the picture on the right, but using only the known astronomical sources of ultraviolet light produces the much thicker structures on the left, and a severe mismatch with the observations. Image is credited to Ben Oppenheimer and Juna Kollmeier.
Computer simulations of intergalactic hydrogen in a “dimly lit” universe (left) and a “brightly lit” universe (right) that has five times more of the energetic photons that destroy neutral hydrogen atoms. Image Credit: Ben Oppenheimer / Juna Kollmeier.

Observations indicate that the ionizing photons from hot, young stars are almost always absorbed by gas in the host galaxy, so they never escape to affect intergalactic hydrogen. The necessary culprit could be the known number of quasars, which is far lower than needed to produce the required light.

“Either our accounting of the light from galaxies and quasars is very far off, or there’s some other major source of ionizing photons that we’ve never recognized,” said Kollmeier in a press release. “We are calling this missing light the photon underproduction crisis. But it’s the astronomers who are in crisis — somehow or other, the universe is getting along just fine.”

Strangely, this mismatch only appears in the nearby, relatively well-studied cosmos. In the early Universe, everything adds up.

“The simulations fit the data beautifully in the early universe, and they fit the local data beautifully if we’re allowed to assume that this extra light is really there,” said coauthor Ben Oppenheimer from the University of Colorado. “It’s possible the simulations do not reflect reality, which by itself would be a surprise, because intergalactic hydrogen is the component of the Universe that we think we understand the best.”

So astronomers are attempting to shed light on the missing light.

“The most exciting possibility is that the missing photons are coming from some exotic new source, not galaxies or quasars at all,” said coauthor Neal Katz from the University of Massachusetts at Amherst.

The team is exploring these new sources with vigor. It’s possible that there could be an undiscovered population of quasars in the nearby Universe. Or more exotically, the photons could be created from annihilating dark matter.

“The great thing about a 400 percent discrepancy is that you know something is really wrong,” said coauthor David Weinberg from Ohio State University. “We still don’t know for sure what it is, but at least one thing we thought we knew about the present day universe isn’t true.”

The results were published in The Astrophysical Journal Letters and are available online.

Posted on by Shannon Hall

A Protostar’s Age Gleaned Only From Sound Waves

A composite image detailing the pre-life story of a star like the Sun, spanning about 10 million years from conception to birth. | © Pieter Degroote (KU Leuven) / background image © ESO

Precisely dating a star can have important consequences for understanding stellar evolution and any circling exoplanets. But it’s one of the toughest plights in astronomy with only a few existing techniques.

One method is to find a star with radioactive elements like uranium and thorium, whose half-lives are known and can be used to date the star with certainty. But only about 5 percent of stars are thought to have such a chemical signature.

Another method is to look for a relationship between a star’s age and its ‘metals,’ the astronomer’s slang term for all elements heavier than helium. Throughout cosmic history, the cycle of star birth and death has steadily produced and dispersed more heavy elements leading to new generations of stars that are more heavily seeded with metals than the generation before. But the uncertainties here are huge.

The latest research is providing a new technique, showing that protostars can easily be dated by measuring the acoustic vibrations — sound waves — they emit.

Stars are born deep inside giant molecular clouds of gas. Turbulence within these clouds gives rise to pockets of gas and dust with enough mass to collapse under their own gravitational contraction. As each cloud — protostar — continues to collapse, the core gets hotter, until the temperature is sufficient enough to begin nuclear fusion, and a full-blown star is born.

Our Sun likely required about 50 million years to mature from the beginning of collapse.

Theoretical physicists have long posited that protostars vibrate differently than stars. Now, Konstanze Zwintz from KU Leuven’s Institute for Astronomy, and colleagues have tested this prediction.

The team studied the vibrations of 34 protostars in NGC 2264, all of which are less than 10 million years old. They used the Canadian MOST satellite, the European CoRoT satellite, and ground-based facilities such as the European Southern Observatory in Chile.

“Our data show that the youngest stars vibrate slower while the stars nearer to adulthood vibrate faster,” said Zwintz in a press release. “A star’s mass has a major impact on its development: stars with a smaller mass evolve slower. Heavy stars grow faster and age more quickly.”

Each stars’ vibrations are indirectly seen by their subtle changes in brightness. Bubbles of hot, bright gas rise to the star’s surface and then cool, dim, and sink in a convective loop. This overturn causes small changes in the star’s brightness, revealing hidden information about the sound waves deep within.

You can actually hear this process when the stellar light curves are converted into sound waves. Below is a video of such singing stars, produced by Nature last year.

“We now have a model that more precisely measures the age of young stars,” said Zwintz. “And we are now also able to subdivide young stars according to their various life phases.”

The results were published in Science.