Planck and the Cosmic microwave background

The anisotropies of the Cosmic microwave background (CMB) as observed by Planck. The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just 380 000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today.

Credit: ESA

Super star projector

There’s a new star in the sky — and it was put there by astronomers using a giant laser. Installed on to one of the telescopes at the European Southern Observatory’s (ESO) Paranal site in Chile this February, the laser projects a ”star” on to the sky, which helps astronomers get a clearer view.

“We project a beam with a diameter of about 50cm, and make a ‘star’ about 90km up in the atmosphere,” explains ESO laser engineer Steffan Lewis. This artificial star acts as a reference point for atmospheric distortion. The light waves it sends back to Earth are “crinkled” by the turbulence and changing density of the atmosphere; this is why stars seem to twinkle. A sensor in the telescope measures the distortion, and very thin deformable mirrors are automatically reshaped to compensate.

Since the laser was installed, astronomers have observed distant objects such as the dwarf planet Haumea and radio galaxy Centaurus A. “By seeing more clearly into the atmosphere, you get very sharp images,” explains Lewis. Or, as we say: everything is better with lasers.

A tale of galactic collisions

When we look into the distant cosmos, the great majority of the objects we see are galaxies: immense gatherings of stars, planets, gas, dust, and dark matter, showing up in all kind of shapes. This Hubble picture registers several, but the galaxy catalogued as 2MASX J05210136-2521450 stands out at a glance due to its interesting shape.

This object is an ultraluminous infrared galaxy which emits a tremendous amount of light at infrared wavelengths. Scientists connect this to intense star formation activity, triggered by a collision between two interacting galaxies.

The merging process has left its signs: 2MASX J05210136-2521450 presents a single, bright nucleus and a spectacular outer structure that consists of a one-sided extension of the inner arms, with a tidal tail heading in the opposite direction, formed from material ripped out from the merging galaxies by gravitational forces.

The image is a combination of exposures taken by Hubble’s Advanced Camera for Surveys, using near-infrared and visible light. A version of this image was submitted to the Hubble’s Hidden Treasures image processing competition by contestant Luca Limatola.

Credit: ESA/Hubble & NASA

NASA’s Fermi, Swift See ‘Shockingly Bright’ Burst

A record-setting blast of gamma rays from a dying star in a distant galaxy has wowed astronomers around the world. The eruption, which is classified as a gamma-ray burst, or GRB, and designated GRB 130427A, produced the highest-energy light ever detected from such an event.

“We have waited a long time for a gamma-ray burst this shockingly, eye-wateringly bright,” said Julie McEnery, project scientist for the Fermi Gamma-ray Space Telescope at NASA’s Goddard Space Flight Center in Greenbelt, Md. “The GRB lasted so long that a record number of telescopes on the ground were able to catch it while space-based observations were still ongoing.”

The burst subsequently was detected in optical, infrared and radio wavelengths by ground-based observatories, based on the rapid accurate position from Swift. Astronomers quickly learned that the GRB was located about 3.6 billion light-years away, which for these events is relatively close.

Gamma-ray bursts are the universe’s most luminous explosions. Astronomers think most occur when massive stars run out of nuclear fuel and collapse under their own weight. As the core collapses into a black hole, jets of material shoot outward at nearly the speed of light.

The jets bore all the way through the collapsing star and continue into space, where they interact with gas previously shed by the star and generate bright afterglows that fade with time.

If the GRB is near enough, astronomers usually discover a supernova at the site a week or so after the outburst.

“This GRB is in the closest 5 percent of bursts, so the big push now is to find an emerging supernova, which accompanies nearly all long GRBs at this distance,” said Goddard’s Neil Gehrels, principal investigator for Swift.

Ground-based observatories are monitoring the location of GRB 130427A and expect to find an underlying supernova by midmonth.

Explanation:

The 1st animation: The maps in the animation show how the sky looks at gamma-ray energies above 100 million electron volts (MeV) with a view centered on the north galactic pole. The first frame shows the sky during a three-hour interval prior to GRB 130427A. The second frame shows a three-hour interval starting 2.5 hours before the burst, and ending 30 minutes into the event. The Fermi team chose this interval to demonstrate how bright the burst was relative to the rest of the gamma-ray sky. This burst was bright enough that Fermi autonomously left its normal surveying mode to give the LAT instrument a better view, so the three-hour exposure following the burst does not cover the whole sky in the usual way.

The 2nd animation: This animation shows a more detailed Fermi LAT view of GRB 130427A. The sequence shows high-energy (100 Mev to 100 GeV) gamma rays from a 20-degree-wide region of the sky starting three minutes before the burst to 14 hours after. Following an initial one-second spike, the LAT emission remained relatively quiet for the next 15 seconds while Fermi’s GBM instrument showed bright, variable lower-energy emission. Then the burst re-brightened in the LAT over the next few minutes and remained bright for nearly half a day.

Credit: NASA/Swift/Stefan Immler

The Whirlpool Galaxy Like You’ve Never Seen it Before

Where do we come from? This is the sort of big question that keeps people up at night, and NASA funded. If you are a star, however, the answer is easy: you come from a big cloud of gas. As astronomers, if we want to understand what controls properties of stars — what makes them big, small, clustered, or isolated– we can start by looking at the gas that will make them.

This paper presents a detailed study of the gas in M51, the Whirlpool galaxy. This system is actually two galaxies, but this paper focuses on the larger, main spiral (NGC 5194) in this interacting pair. This galaxy is relatively close by (20 million light years away),  massive (~150 billion solar masses), and quite well-studied: astronomers have looked at it in wavelengths from radio to near-infrared, optical and ultraviolet.  The combined resolution and sensitivity of these new millimeter observations (the J=1-0 rotational transition of the carbon monoxide molecule) allow the authors to detect for the first time individual molecular clouds in this galaxy, the objects from which stars and star clusters are born. Below is an image of M51 from this study showing the gas surface density (the amount of gas along our line of sight) from small amounts (dark blue) to large amounts (bright pink), all representing the fuel required to make the next generation of stars in this galaxy.

So what does it take to make an image like this? ALMA? Not quite. M51, with a declination of +47 degrees, is a galaxy that ALMA (the Atacama Large Millimeter Array, located in Chile at a latitude of 23 degrees South) will find very difficult to observe. Instead, the authors used the Plateau de Bure Interferometer (PdBI) and the IRAM 30m radio telescope to detect gas clouds as small as 40 parsecs across. The image above is a mosaic combining 60 pointings of PdBI with IRAM observations over the same region. But isn’t one telescope enough for the job of observing M51? Why take the time to observe it twice?

The answer is that interferometers (arrays of two or more telescopes which work together to act like a telescope with a diameter equal to the separation between antennas) by themselves have a big problem for big objects like M51. Although interferometers give us the advantage of higher resolution, that is not whole story– not only does the antenna separation determine the resolution, it also sets the size scales that you are sensitive to, acting like a high-pass filter for spatial frequencies. As shown in the figure below, a pair of antennas in an interferometer resolve ‘fringes‘ on the sky representing the resolution of that antenna pair (a function of the frequency of the observations and the spacing of the antennas). Different spacings and orientations from the combinations of many antenna-pair fringes contribute to making your beam– the tiny white dot in the bottom left corner of the above image, and the interferometric equivalent of the point-spread function (PSF). The problem is that flux from structures larger than the largest fringe that goes into making this beam will be lost. Since the shortest antenna spacing yields the largest fringe, and the antenna spacing cannot be smaller than the size of the telescope (get too close and the antennas will start bumping into and blocking each other), there is a maximum size scale that you can detect flux from.

How can we get that flux back? Use a single dish telescope! These telescopes are sensitive to the flux on all size scales larger than the resolution of their dish. By combining the data from an interferometer with single dish data, you can recover all of the flux from an object, and still observe it at high resolution. This synergy is why the most effective radio and millimeter interferometers all have a single-dish buddy: the Very Large Array (VLA) has the Green Bank Telescope (GBT), the PdBI (which took these images) has IRAM, and ALMA will have both a compact array and several ‘total power’ single dishes.

So now that you have a high-resolution picture of almost all of the gas clouds in M51, what do you do with it? This paper focuses on comparing (correlating) the location and amount of this gas with other tracers of galaxy properties. This includes tracers of different phases of the interstellar medium (the ISM, or gas in a galaxy at all temperatures, from plasma to neutral to molecular), tracers of star formation, and tracers of the existing stellar populations.

The PdBI Arcsecond Whirlpool Survey (PAWS). I. A Cloud-Scale/Multi-Wavelength View of the Interstellar Medium in a Grand-Design Spiral Galaxy →

Markarian galaxies

The Markarian galaxies are a class of galaxies that have nuclei with excessive amounts of ultraviolet emissions compared with other galaxies. Benjamin Markarian drew attention to these types of galaxies starting in 1963. The nuclei of the galaxies had a blue colour that in a star would be classed from A to F. This blue core did not match the rest of the galaxy. The spectrum in detail tends to show a continuum that Markarian concluded was produced non-thermally. Most of these have emission lines and are interesting because of their energetic activity.

In 1964 Markarian decided to search for this kind of galaxy. The First Byurakan Survey commenced in 1965 using the Schmidt telescope at the Byurakan Astrophysical Observatory. The telescope used a 132 cm mirror and 102 cm correcting plate. When this started it was the largest telescope to have a full aperture objective prism. The purpose of the survey was to find galaxies with an ultraviolet excess. The optics used were corrected for blue violet. Prisms in this had a low dispersion of 180 nm/mm in order not to spread out the galactic core spectrum too much and confuse it with other objects. This permitted classification of galaxies with magnitudes down to 17.5. Seventy galaxies with UV-continuum appeared on lists, and the term “Markarian galaxies” came into use.

Two more lists brought the number of galaxies up to 302 in 1969. The FBS continued observations till 1978 with a full spectra survey at high galactic latitudes. 1980 saw the completion of plate analysis and picking the objects that would be included. Twelve more papers with objects from the First Byurakan Survey brought the list up to 1500 galaxies.

 Credit: ESO

The Very Large Telescope array (VLT) is the flagship facility for European ground-based astronomy at the beginning of the third Millennium. It is the world’s most advanced optical instrument, consisting of four Unit Telescopes with main mirrors of 8.2m diameter and four movable 1.8m diameter Auxiliary Telescopes. The telescopes can work together, to form a giant ‘interferometer’, the ESO Very Large Telescope Interferometer, allowing astronomers to see details up to 25 times finer than with the individual telescopes. The light beams are combined in the VLTI using a complex system of mirrors in underground tunnels where the light paths must be kept equal to distances less than 1/1000 mm over a hundred metres. With this kind of precision the VLTI can reconstruct images with an angular resolution of milliarcseconds, equivalent to distinguishing the two headlights of a car at the distance of the Moon.

The 8.2m diameter Unit Telescopes can also be used individually. With one such telescope, images of celestial objects as faint as magnitude 30 can be obtained in a one-hour exposure. This corresponds to seeing objects that are four billion (four thousand million) times fainter than what can be seen with the unaided eye.

The large telescopes are named Antu, Kueyen, Melipal and Yepun. For more information about the meaning of these names, click here.

The VLT has made an undisputed impact on observational astronomy. It is the most productive individual ground-based facility, and results from the VLT have led to the publication of an average of more than one peer-reviewed scientific paper per day. VLT contributes greatly to making ESO the most productive ground-based observatory in the world. The VLT has stimulated a new age of discoveries, with several notable scientific firsts, including the first image of an extrasolar planet (eso0428), tracking individual stars moving around the supermassive black hole at the centre of the Milky Way (eso0846), and observing the afterglow of the furthest known Gamma-Ray Burst.

Hawc gamma-ray telescope captures its first image

A new set of “eyes” to capture the Universe’s highest-energy particles and light has snapped its first image.

The High-Altitude Water Cherenkov Observatory or Hawc, high on a Mexican plain, now holds the record for the highest-energy light it can capture.

The image - of the shadow cast by the Moon as it blocks the light and particles - was shown off at a meeting of the American Physical Society.

Hawc is currently made of 30 detectors, but by 2014 will comprise some 300.

Each one is a 7.3m-diameter, 4m-high tank filled with pure water.

They dot the landscape at an altitude of 4,100m in a national park near the Mexican city of Puebla.

But they do not capture the cosmic rays and gamma rays directly.

When the cosmic rays and gamma rays smash into molecules in the Earth’s atmosphere, they set off a cascade of other fast-moving particles.

It is these that the “Cherenkov” detectors actually track.

Faster than light

While the speed of light in a vacuum cannot be exceeded, the speed in matter can be much slower.

When the fast-moving particles created in the atmosphere break this speed limit inside the water of the Hawc tanks, they give off flashes of light that detectors at the tanks’ bottoms can catch.

Cherenkov telescopes such as the Hess array in Namibia or the Magic facility in the Canary Islands catch this process directly from the atmosphere when the particles first arrive at Earth.

But while Hawc catches fewer of these events high in the atmosphere, it can survey more in a given night - or day, said Hawc collaboration member Tom Weisgarber of the University of Wisconsin-Madison.

“We’re very complementary to these other instruments - but we see a very large fraction of the sky,” he told BBC News.

“Hawc doesn’t need to point in one location, and it’s unaffected by the Sun, the Moon, the weather or anything - it just depends on the atmosphere being there.”

It also claims the crown for highest-energy light we can detect - up to 100 TeV, or tens of trillions of times more energetic than the visible light we can see.

Particles and light with these blistering energies give insights into the most violent processes the cosmos hosts, from the leftovers of supernovas to supermassive black holes eating matter.

Only by catching them can we understand just how these regions create them.

But Hawc is just starting its mission, and to make sure that its first 30 detectors are working as expected, the team snapped an image exactly where it did not expect any cosmic rays - the Moon’s shadow.

A fuller array of 100 detectors should be up and running by August.

“That’s when we’ll really be able to start doing some really interesting science,” Mr Weisgarber said.

Credit: Jason Palmer

Just how big was the Big Bang? Discover how scientists have calculated the exact volume of the noise created at the birth of the Universe.

Like many positive terms, the phrase “big bang” originated as a pejorative. Fred Hoyle coined the term in 1949 as a way of deflating the concept of an expanding universe. It stuck, even after Edwin Hubble showed that 13.7 billion years ago, all of the matter in our massive universe was indeed compacted into “one superdense ball.” Astronomers have also figured out that the volume of the big bang was only 120 decibels, about the loudness of your average rock show (though how there might have been sound without an atmosphere escapes me). There is some irony in Hoyle’s dig: the “big bang” wasn’t particularly big, and wasn’t much of a bang, but it happened.

Positrons Galore

Antimatter is rare in the universe today. As far as we know, all relic antimatter produced in the big bang disappeared long ago in annihilation reactions with matter particles. What this means is that any antimatter particles that we can detect in the flux of energetic cosmic rays near Earth must have been created by “new” sources within our Milky Way Galaxy. (Antimatter particles from extragalactic sources are also conceivable, but they are exceedingly unlikely to make it to Earth before losing all their energy or annihilating.) Because there is a limited amount of energetic antimatter from space raining down upon the Earth, antiparticles serve as unique messengers of high-energy phenomena in the cosmos, or signatures of exotic new physics.

The flux of high-energy particles near Earth (cosmic rays) can come from many sources. “Primary” particles (green) come from the original cosmic-ray source (typically, a supernova remnant). “Secondaries” (yellow) come from these particles colliding with interstellar gas and producing pions and muons, which decay into electrons and positrons. A third, interesting possibility is that electrons and positrons (purple) are created by the annihilation of dark matter particles, denoted by χ˜ in the figure, in the Milky Way and its halo. Note that for illustrative purposes the background image used here is of Andromeda, a typical spiral galaxy, roughly similar to ours.

For more information: http://physics.aps.org

Credit: Stephane Coutu, Institute for Gravitation and the Cosmos, Departments of Physics and of Astronomy and Astrophysics, Pennsylvania State University

‘Comet Galaxy’

While looking at the galaxy cluster Abell 2667, astronomers found an odd-looking spiral galaxy that ploughs through the cluster after being accelerated to at least 3.5 million km/h by the enormous combined gravity of the cluster’s dark matter, hot gas and hundreds of galaxies.

Light and dust in a nearby starburst galaxy

Visible as a small, sparkling hook in the dark sky, this beautiful object is known as J082354.96+280621.6, or J082354.96 for short. It is a starburst galaxy, so named because of the incredibly (and unusually) high rate of star formation occurring within it.

One way in which astronomers probe the nature and structure of galaxies like this is by observing the behaviour of their dust and gas components; in particular, the Lyman-alpha emission. This occurs when electrons within a hydrogen atom fall from a higher energy level to a lower one, emitting light as they do so. This emission is interesting because this light leaves its host galaxy only after extensive scattering in the nearby gas — meaning that this light can be used as a pretty direct probe of what a galaxy is made up of.

The study of this Lyman-alpha emission is common in very distant galaxies, but now a study named LARS (Lyman Alpha Reference Sample) is investigating the same effect in galaxies that are closer by. Astronomers chose fourteen galaxies, including this one, and used spectroscopy and imaging to see what was happening within them. They found that these Lyman-alpha photons can travel much further if a galaxy has less dust — meaning that we can use this emission to infer how dusty the source galaxy is.

The LARS study relies heavily on the high resolving power of Hubble. When Hubble is decommissioned, no telescope will be able to make observations like this in the far ultraviolet part of the spectrum — meaning that small, glittering galaxies imaged and probed by studies like LARS may give us some of the most detailed data we have to work with for some time to come.

Credit: ESA/Hubble & NASA, M. Hayes

Star birth in Cepheus

Cep OB 3b is rich young cluster located in the northern constellation of Cepheus. This image was created by combining individual images observed through four different filters on the 0.9 meter telescope at Kitt Peak: blue, visual (cyan), near infrared (orange) and an emission line of hydrogen (red). The brightest yellow star near the center of the image is a foreground star, lying between us and the young cluster. The other bright stars are the massive young stars of the cluster that are heating the gas and dust in the cloud and blowing out cavities. Surrounding these massive cluster stars are thousands of smaller young stars that may be in the process of forming planetary systems.

Full Article→

Credit: T.A. Rector (University of Alaska Anchorage), T. Allen (University of Toledo) and WIYN/NOAO/AURA/NSF

Star on a Hubble diet

Left: ACS WFC image of NGC 6357 with Pismis 24-1 in the centre (the brightest star). Middle: Looking closer at Pismis 24-1 with Hubble’s ACS High Resolution Channel it becomes clear that it is in reality two stars.Right: ACS HRC image close-up showing the two stars of Pismis 24-1. It was thought to have an incredibly large mass of 200 to 300 solar masses. New NASA/ESA Hubble measurements of the star, have, however, resolved Pismis 24-1 into two separate stars, and, in doing so, have “halved” its mass to around 100 solar masses.

Credit:

NASA, ESA and Jesœs Ma­z Apellÿniz (Instituto de astrof­sica de Andaluc­a, Spain). Acknowledgement: Davide De Martin (ESA/Hubble)

Through the Blinds

Cassini gazes down through the dark side of Saturn’s rings toward the softly glowing planet. The night side southern hemisphere is lit by sunlight reflecting off the opposite side of the rings. The planet’s shadow slices diagonally across the scene.

This view was acquired from about 23 degrees above the ringplane. The sliver of Saturn’s sunlit crescent is partly overexposed as seen through the Cassini Division, a region where there is less material to block or scatter incoming light.

Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were taken with the Cassini spacecraft wide-angle camera on Sept. 11, 2006 at a distance of approximately 1.1 million kilometers (700,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 151 degrees. Image scale is about 60 kilometers (37 miles) per pixel.

Credit: NASA/JPL/Space Science Institute