Astronomy & Science

Amateurs Given David Dunlap Observatory

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After serving as caretakers of Canada's largest telescope for the past six years, volunteers from the RASC's Toronto club have been given the historic facility outright.

Think of it as taking professional-amateur collaboration to a new dimension. Dedicated stargazers have long proven their worth for tracking dust storms on Mars, chasing down near-Earth asteroids, and compiling light curves of variable stars. Now they're getting the chance to run a professional observatory.

David Dunlap Observatory

David Dunlap Observatory, located in suburban Toronto, boasts what was once the world's second-largest telescope.
John H. Martin / Wikipedia Commons

On April 15th, the Royal Astronomical Society of Canada announced that its 900-member Toronto club is taking ownership of historic David Dunlap Observatory, located in the Toronto suburb of Richmond Hill. The observatory and its administrative building are being donated by Corsica Development, which purchased the facility and 190 acres of land around it from the University of Toronto in 2009. Corsica is also giving 100 acres of the property to the town, which will keep it from being developed.

"We’re honored by this incredibly generous gift," says Paul Mortfield, president of RASC's Toronto Centre, in a press release announcing the transfer. All parties involved have been working toward this agreement since the university sold the observatory for $70 million to establish the Dunlap Institute for Astronomy and Astrophysics. That's when the RASC's volunteers, who had been involved in the observatory's outreach programs for decades, stepped in to maintain and operate the historic facility.

The observatory got its start in 1935 after the widow of David Alexander Dunlap, a wealthy mining executive and astronomy enthusiast, provided the funds for construction. Its premier instrument, a 1.9-meter (74-inch) reflector, was then the second largest in the world and remains the largest telescope in Canada.

Perseid party at David Dunlap Observatory

David Dunlap Observatory is the site of many public astronomy events, such as this gathering during the Perseid meteor shower. In the background is the dome for the observatory's 74-inch (1.9-m) reflector — the largest telescope in Canada.
RASC Toronto Centre

But urban growth long ago made the site unsuitable for most types of observational research, and the university's astronomical interests shifted to Algonquin Radio Observatory in central Ontario and to collaborations such as Gemini Observatory and the Atacama Large Millimeter/submillimeter Array in Chile.

Meanwhile, the new owners are looking forward to expanding their outreach and education programs. Improving public access to the property is one goal, in part through improvements to the local transit system, and that will require working collaboratively with the town. Members of the RASC Toronto Centre will also be seeking funding from foundations and private donors to augment the modest funds they already receive from attendees of events at the observatory.

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This Week’s Sky at a Glance, April 17 – 25

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Some daily sky sights among the ever-changing Moon, planets, and stars.

A month after it erupted, the nova in the Sagittarius Teapot continues to fluctuate between about magnitude 4.5 and 6. If it's a "slow nova" it could become even brighter this summer. It's now fairly well up in the south-southeast before the beginning of dawn. See article with charts and up-to-date light curve.


Watch as the Aldebaran-Venus-Pleiades triangle stretches out taller and sideways this week.

Friday, April 17

Every evening Venus continues to stay put at nearly the same spot above the western twilight landscape, while Aldebaran, the Hyades and Pleiades slide farther down to the lower right behind it.

Callisto occults Ganymede among Jupiter's moons. Dark Callisto crosses in front of Ganymede from 9:27 to 9:37 p.m. Eastern Daylight Time. Their combined light will dim by 1.0 magnitude during the middle of this time. Start watching with your scope early to see them moving together into a blend just beforehand.

Saturday, April 18

After dusk, look very high in the west (far to the upper left of Venus) for Pollux and Castor lined up almost horizontally. They're to the lower right of bright Jupiter. Pollux and Castor are the heads of the Gemini twins, now standing almost upright. They form the top of the enormous "Arch of Spring." The Arch's two ends are Procyon to their lower left, and brighter Capella farther to their lower right.

New Moon (exact at 2:57 p.m. EDT).

The waxing crescent Moon poses left of Mercury and Mars very low after sunset, then the Pleiades, then Venus higher up.

The waxing crescent Moon poses left of Mercury and Mars very low after sunset on Sunday the 19th, then the Pleiades on Monday, then Venus on Tuesday higher up. The blue 10° scale as about the width of your fist at arm's length. The Moon is drawn three times its actual apparent size.

Sunday, April 19

Mercury and very faint Mars are near the hairline crescent Moon very low in the west-southwest in bright twilight, as shown at lower right. Bring binoculars.

Monday, April 20

In twilight, look for the sliver of the crescent Moon in the west. It pins the corner of a quadrilateral with Venus, Aldebaran, and the Pleiades, as shown here.

Io eclipses Europa among Jupiter's moons. Io casts its shadow onto Europa this evening from 11:44 to 11:47 p.m. Eastern Daylight Time. Europa will dim by 1.8 magnitudes — a factor of five! — at the middle of these few minutes.

Now that Jupiter is far from opposition, we see shadows in the Jovian system falling far enough sideways that an eclipsed satellite and its eclipser appear widely separated in a telescope's view. So we can see the eclipsed satellite dimming by itself, uncontaminated by the light of the eclipser. (The tables in Sky & Telescope for these events presume that the two satellites appear blended and give their combined magnitude.) See Bob King's article Catch the Last Best Antics of Jupiter’s Moons.

Tuesday, April 21

The waxing crescent Moon shines left of Venus and above Aldebaran in twilight, as shown above.

Far to their lower right, Mercury and faint Mars are within 1.6° of each other this evening and tomorrow evening. Look early with binoculars.

Wednesday, April 22

The Lyrid meteor shower, usually quite weak, should be at its modest peak tonight from about 11 p.m. until the first light of dawn Thursday morning.

Thursday, April 23

It's almost May, but the winter star Sirius still twinkles low in the southwest as twilight fades. How much later into the spring can you keep Sirius in view?

Friday, April 24

The Moon tonight sits on (or near) one side of a big, almost equilateral triangle: bright Jupiter to the Moon's upper left, Pollux upper right of the Moon, and Procyon to the Moon's lower left.

As the Moon waxes past first quarter, it glides under Jupiter and the Sickle of Leo.

As the Moon waxes past first quarter, it glides under Jupiter and the Sickle of Leo.

Saturday, April 25

First-quarter Moon (exact at 7:55 p.m. EDT). Jupiter shines closer to the upper left of the Moon this evening. Jupiter poses directly above the Moon as the night grows late. Although they may look close together, Jupiter is nearly 2,000 times farther away — and 40 times larger in diameter.


Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby; for an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and once you know your way around, the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.

This Week's Planet Roundup Jupiter on April 1, 2015

On April 1st, Io and its shadow were crossing Jupiter when Christopher Go took this image at 11:17 UT. South is up. The South Equatorial Belt continues to be a little wider and less dark than the North Equatorial Belt. The Red Spot Hollow around the spot is wide and light-colored, and the Red Spot's wake continues to be turbulent. Far below, in the narrow, broken North Temperate Belt, the thin, dark red barge has become more elongated than it was a few weeks ago. These stacked-video images have been sharpened and contrast-boosted.

Jupiter on April 6, 2015, by Christopher Go

How many changes can you find on this image taken five days later, on April 6th?

And again, April 13th.

And again, April 13th.

Mercury (about magnitude –1.4) is emerging from deep in the glow of sunset. About 20 or 30 minutes after sunset, look for it just above the horizon very far to the lower right of Venus. Mercury gets a little higher and easier every day. Mars, much fainter, is in the close vicinity.

Venus (magnitude –4.1, in Taurus) blazes in the west during and after twilight — the brilliant "Evening Star." It doesn't set in the west-northwest until nearly two hours after dark. In a telescope Venus is still small and gibbous, but each week it's growing and thinning as it approaches us in its orbit.

Mars (magnitude +1.4) is deep in the sunset near Mercury — which is more than 10 times brighter. Early this week, Mars is to Mercury's upper left. They appear closest together on April 21st and 22nd, separated by 1.6° or less, with Mars to Mercury's left. Bring binoculars!

Jupiter (magnitude –2.2, in Cancer) shines high in the south as the stars come out, and less high in the southwest after dark. It's the second-brightest point of light in the sky, after Venus. Don't expect to see nearly the detail with your eye that video-frame stacking with large amateur telescopes can bring out, as in the fine images here.

Saturn (magnitude +0.2, just above the head of Scorpius) rises around 10 or 11 p.m. daylight-saving time and is highest in the south in the middle of the early-morning hours. Below or lower left of Saturn (by 9°) is orange Antares, not as bright. The next brightest star in the area is Delta Scorpii, half as far from Saturn. Delta Sco is now in its 15th year of outburst!

Uranus and Neptune are deep in the glow of dawn.


All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.


“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”

— Neil deGrasse Tyson, 2014.


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Abu Dhabi Astronomy

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Abu Dhabi Astronomy


Flat 1202 Block D
Khaleej Al Arabi St.
Abu Dhabi
United Arab Emirates


Alejandro Palado






Abu Dhabi Astronomy was created to cater all lovers of Sky, it serves the public in promoting all areas of astronomy.

The post Abu Dhabi Astronomy appeared first on Sky & Telescope.

Ancient Galaxies Seen Dying Inside-Out

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Astronomers have found massive galaxies 3 billion years after the Big Bang that are dying from the inside out.

The most massive galaxies in today’s universe are bulbous ellipticals easily 100 times the mass of our spiral Milky Way. These galaxies are essentially “red and dead” — they built up about 80% of their stars more than 6 billion years ago, so any stars shining today are old and rust-colored. They generally have no star formation today.

But 10 billion years ago, at the peak of star formation across the cosmos, these galaxies were ablaze with new, young stars. Between then and now, those stars fizzled out.

massive galaxy evolution

Star formation in what are now "dead" massive galaxies sputtered out billions of years ago. New observations reveal that about 10 billion years ago, these galaxies still were forming stars on their outskirts, but not in their interiors, a process illustrated here (time goes from left to right). The blue regions are where star formation is in progress, while red regions have only older, redder stars.
Credit: ESA / Hubble and ESO

Last year, two teams found compact, star-forming galaxies in this early cosmic period. Stars in these galaxies are packed as densely as those in so-called compact cores, galaxies in the early universe 10 times the mass of the Milky Way and where star formation has already ceased. That correlation suggests the star-forming compact galaxies became the compact cores. They in turn likely grew into today’s most massive ellipticals by usurping stars from much smaller galaxies, accreting stars onto their outskirts as they tore up and ate their smaller siblings.

But it seems there’s more than one way to grow a big galaxy.

In the April 17th Science, Sandro Tacchella (ETH Zurich, Switzerland) and colleagues report their analysis of 22 star-forming galaxies 10 to 11 billion years ago (average redshift 2.2). These galaxies are not as dense as the compact cores, but the most massive rival them in number of stars. Using images from the Hubble Space Telescope and spectra from the SINFONI instrument on the ESO’s Very Large Telescope in Chile, the team tracked star formation inside the galaxies and found that, in the most massive ones, star formation is shutting down — and from the inside out. Essentially, these massive galaxies contain dead centers surrounded by star-forming envelopes.

These galaxies, unlike the compact ones, churn out stars for longer, retaining a youthful glow for another 2 or 3 billion years. So instead of beefing up their edges by merging with punier galaxies, they grew by forming their own stars. By about 7 billion years ago (redshift of 1), they’ll also be red and dead.

At that point, it’s hard to distinguish which galaxies started out as compact cores and which ones started with an extended, star-forming envelope, says Guillermo Barro (University of California, Santa Cruz), who helped discover the early, compact galaxies reported last year. Essentially, there are two distinct galactic breeds that can both grow into today’s massive ellipticals.

Tacchella’s team doesn’t know why their galaxies are dying inside-out, but the astronomers suspect it’s an internal process. Perhaps a black-hole-spurred outflow from the galaxies’ centers quenches star formation in the inner regions — the most massive galaxies the team looked at do have fast nuclear outflows. Or perhaps star formation shuts off when the local environment hits a critical density of stars — the observations confirm that the local stellar density is very high when the shutdown starts. For now it’s a chicken-and-egg question.


Reference: S. Tacchella et al. “Evidence for mature bulges and an inside-out quenching phase 3 billion years after the Big Bang.” Science, April 17, 2015.

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Rosetta’s Comet Campaign Wants YOU!

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Participate in a world-wide campaign to observe and photograph Comet 67P/C-G as it approaches and recedes from the Sun with Rosetta in tow. Your observations matter.

Comet recovered!

The fun begins! A team of astronomers recovered Comet 67P/C-G on April 14 after solar conjunction under difficult conditions (low altitude, moonlight) from Chile. It was magnitude 16.8.
Jean François Soulier, Jean Gabriel Bosch, CAO, San Pedro de Atacama

Just because there's a billion-dollar-plus spacecraft mission examining every nook and cranny of Rosetta's comet doesn't mean amateur astronomers can't play an important role in its study, too. To tap into the skills of amateurs and professionals alike, the Rosetta Worldwide Ground-based Observing Program was initiated last year.

At the time, Comet 67P/Churyumov-Gerasimenko was little more than a 23rd-magnitude blip. But now that the comet is emerging from solar conjunction and brightening, the campaign is moving into high gear. Time to dust off that scope!

You wouldn't think an 8-inch Dob under the quivering blanket of Earth's atmosphere could add to the our understanding of 67P/C-G, but amateurs have several advantages:

* They're not tied to a schedule or competing for time at a large observatory like most professional astronomers. Amateurs are free to spend as much time as needed making visual observations and sketches, taking comet photos, and recording spectra.

* Ground-based observations, both from amateurs and professionals, provide a "big picture" perspective complementing the up-close, in situ measurements from Rosetta.

* Astronomy hobbyists form a global network of sky enthusiasts. If there's a sudden change in a comet's behavior, amateurs are often among the first to report the news, alerting professionals to take a closer look with more powerful instruments.

* Amateurs can observe comets close to the Sun without fear of damaging the more sensitive instruments used by professional astronomers.

Campaign leads

Padma Yanamandra-Fisher (left) and Colin Snodgrass, the coordinators of the Comet 67P amateur and professional ground-based campaigns.
Courtesy photos

The two-pronged campaign will serve as a clearinghouse and database for amateurs and professionals alike. Colin Snodgrass, astronomer and planetary scientist at The Open University, heads up the pro side. NASA's Jet Propulsion Lab oversees the amateur campaign coordinated by Padma Yanamandra-Fisher, Senior Research Scientist at the Space Science Institute.

Yanamandra-Fisher was a key figure in the C/2012 S1 (ISON) and C/2013 A1 (Siding Spring) campaigns, working closely with amateurs to encourage to them share and contribute observations.

Having joined in both those earlier efforts, I can vouch for the participants' enthusiasm and excitement at being part of a group effort. All contributions were accepted: photos, magnitude estimates, maps, spectra, sketches, verbal descriptions, you name it. Not only did the data flow daily, but members were more than willing to answer questions or confirm an observation.

One puzzle piece at a time

Sketch of comet 67P showing a bright nucleus, compact coma, and short tail made during the December 1982 apparition. Even simple sketches like this one can help tell 67P's story.
Bob King

By following the stream of commentary and images, I not only learned more about comets but was able to compare my observations with others, sharpening my observing skills in the process.

Let's just say it was a blast, and I felt like my tiny contribution mattered. Yours will, too.  Amateur astronomers can sign up here for the new campaign. Once registered, you'll start receiving updates from your fellow observers at the PACA (Pro-Amateur Collaborative Astronomy) Rosetta67P Facebook group. You'll also contribute your observations there.

Professional astronomers can go to the Rosetta Campaign site or e-mail Colin Snodgrass.

67P is currently crossing from Aquarius into Pisces and just beginning to emerge from the solar glare for observers in the southern hemisphere. With an estimated magnitude at around +16, the comet will still be a very difficult object to see visually, but well within the range of amateur astrophotography. Solar elongation increases to 37° in mid-May with the comet a magnitude brighter and ripe for a portrait before the start of dawn.

En route to your eyes

Comet 67P/Churyumov-Gerasimenko's path during the time of best viewing from mid-July to November. The comet will be visible low in the eastern sky shortly before the start of dawn for observers across both hemispheres.
Chris Marriott's SkyMap

Northern skywatchers will have to be patient. By mid-July, 67P will have brightened to around magnitude +13.4 — within range of 8- and 10-inch telescopes from dark skies — and beckon early morning risers from its perch near the Hyades in Taurus some 10° high at dawn's start.


Light curve showing brightness estimates made by comet observers (black dots) and a prediction of Comet 67P's brightness from Seiichi Yoshida's Weekly Comet Information site. In this analysis, the comet may wax as bright as 11th magnitude. Periodic comets like 67P/C-G often lag in brightness early in an apparition and then brighten more quickly at and shortly after perihelion (purple line). Click image to visit the site.
Seiichi Yoshida

According to JPL's Horizons site and magnitudes based on orbital elements from the Minor Planet Center, the comet continues gaining altitude, passing perihelion on August 13 in Gemini with a peak brightness around magnitude +13. Or maybe not. Comets are notorious for ignoring predictions, so who knows how bright 67P might become?

Solar snap the whip

The portion of Comet 67P/C-G's orbit when things really start to heat up. Notice the descriptive temperature indicators. Perihelion occurs on August 13.

67P tracks from Cancer through Leo as summer mellows into fall, slowly fading as it departs both Sun and Earth. Come mid-December, the comet will return to its slumbers at magnitude +15. With your eyes, telescope and camera, you can help tell its story while playing a part in one of humanity's grandest adventures.

Learn the Secrets of Stargazing from expert observer Becky Ramotowski!

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Come to NEAF This Weekend!

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This weekend features the world's largest astronomy expo, the Northeast Astronomy Forum (NEAF), in Suffern, New York.

The Sky & Telescope office is seeing a flurry of activity as our editors prepare for the annual pilgrimage to Suffern, New York, for the Northeast Astronomy Forum (NEAF) this coming weekend, April 18 and 19th. Billed as “America’s Premiere Astronomy Expo,” NEAF is celebrating its 24th year.

Northeast Astronomy Forum

A scene from NEAF 2014.
Sean Walker

Founded by the Rockland Astronomy Club, NEAF began as a small affair held in a cozy corner of the campus of Rockland Community College. Now it fills the college’s sports arena with the world’s largest trade show for amateur astronomy gear, in addition to presenting all-day astronomy programs for the public.

This year’s show will have more than 110 vendors and exhibitors providing lots of cool new products from telescopes to cameras. Many vendors offer discounts at the show.

NEAF also includes two full days of workshops and lectures by renowned speakers, including S&T’s own senior editor J. Kelly Beatty, who will discuss Pluto and NASA’s New Horizons mission, which is on the cusp of reaching this distant world after 9 years in space.

Marc Rayman, mission director at NASA/JPL and chief engineer for the Dawn mission to Vesta and Ceres, will present a mission update to attendees.

Other speakers include Bill Gerstenmaier, director of NASA’s human space flight program, Alan Hershfield, author and professor in the physics department of University of Massachusetts, and Christopher Go, amateur astrophotographer specializing in Jupiter studies.

NEAF isn’t just about booths and talks. If the Sun cooperates there will be a solar star party outside all day. Professionals and volunteers will share an array of telescopes and filters for close-up looks at our lively Sun.

If you’re in town early, the Northeast Astro Imaging Conference (NEAIC) will be held at the Crown Plaza hotel in Suffern on Thursday and Friday ((the 16th and 17th), where astrophotographers will gather to learn the latest imaging tips and techniques from the masters, including Jerry Lodriguss. Be sure to check it out.

We’re looking forward to making the journey to NEAF again this year, and we hope to see you at our booth!

P. S.: Stop by our booth — we’ll have 20%-off coupons for every item in Sky & Telescope’s online store.

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Dawn Maps Ceres in False Color

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Thanks to NASA’s Dawn spacecraft, we’re finally seeing more of the asteroid Ceres than a fuzzy ball. This mosaic, assembled from images taken in blue, green, and infrared spectral filters, shows the dwarf planet’s surface in false color:

 NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

The color scheme in this map is inverted from reality: the version JPL released assigns the short, bluer wavelengths to be red, and the long, infrared wavelengths (which the human eye can't see) to be blue. That seemed a wee daffy to me, so I asked what was up. Turns out the camera team wanted the map to look unreal: it's too early in the mission to unambiguously separate all the things that influence the surface's apparent color, and when the team made a map with a different color scheme, it led to misleading interpretations even among the team's own members. So instead they decided to emphasize the "false" in false-color and forestall confusion.

But the colors do help us pick out surface differences. The asteroid’s surface definitely has variety; as the press release from JPL explains, the images suggest that Ceres was once more active geologically. That’s not surprising: between 17% and 27% of Ceres’ mass is water, and planetary scientists have speculated whether it might have had (or even still have?) a subsurface water ocean driving geology up top. There are also fewer large craters than expected.

Dawn has only just begun its investigation, so we’ll have to wait until it spirals closer to the asteroid’s surface to better understand Ceres.

You can read more about the Dawn mission in our April 2015 issue. You can also explore Ceres as a globe in this web tool adapted by astronomy enthusiast Grzegorz Czepiczek. And don't forget about the mission director's Dawn Blog, either.


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A Ring-Shaped Spyglass to the Early Universe

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A rare type of gravitational lens offers astronomers a close look at a young, dusty galaxy manufacturing hundreds of stars a year.

Einstein Ring of Fire

It might not look like it, but this fiery ring was originally in the form of a dusty disk galaxy named SDP.81. This composite combines ALMA and Hubble Space Telescope images of the rare gravitational lens known as an Einstein Ring. The diffuse blue light at the center of the ring comes from starlight in the intervening lensing galaxy, as seen with the Hubble. The orange ring of distorted light comes from dust and carbon monoxide gas in the more distant SDP.81.
ALMA (NRAO / ESO / NAOJ); B. Saxton (NRAO / AUI / NSF); Hubble (NASA / ESA); T. Hunter (NRAO)

Within the Hydra constellation, now to the south in northerners’ evening sky, there exists an almost perfect ring of light about 3 arcseconds across. This weirdly symmetric phenomenon is a rare gravitational lens known as an Einstein Ring, the result of a near-perfect alignment between a very distant galaxy, a not-quite-so-distant galaxy, and us.

Einstein Ring

This image includes only ALMA-imaged wavelengths, zeroing in on cosmic dust glowing in the distant, gravitationally lensed galaxy SDP.81.

The background galaxy is informally known as SDP.81 (which rolls slightly more easily off the tongue than its formal name, H-ATLAS J090311.6+003906). Its light traveled for 12 billion years to arrive at Earth, but the journey wasn’t uneventful — 8 billion years into its flight, it encountered a massive elliptical galaxy. The galaxy’s gravity acted as a lens, bending the path of the background light to form a ring of emission.

Though these lensed rings are named for Einstein, Einstein himself declared in 1936, “Of course, there is no hope of observing this phenomenon directly.” His pessimism was warranted since he was only considering stars, not galaxies — he reasoned that such perfect alignment would be too rare to glimpse in the real world, and even if visible, he thought the circles’ small angular size was beyond telescopes’ capabilities.

Partial Ring of Fire

This image shows only the highest-resolution detail captured by ALMA, revealing details 23 milliarcseconds, or roughly 100 light-years, apart.

The lensed ring of SDP.81 is small. Your finger held out at arm’s length covers 1°, or 3600 arcseconds. The best ground-based telescopes can make out details separated by 1 arcsecond under good conditions. The Hubble Space Telescope can resolve details 10 times finer, good enough to see the ring itself, but not enough to study it in detail.

Now the Atacama Large Millimeter/submillimeter Array (ALMA) has gone one step further, turning its dishes to SDP.81’s known Einstein ring during testing of its “long baseline” capability. During this time, the antennas’ maximum separation was 15 kilometers (9 miles), offering unprecedented magnifying power. ALMA spied submillimeter-wavelength details in the ring just 23 milliarcseconds (about a millionth of a degree) across.

Combined, the array’s resolving power and nature’s gravitational lens give astronomers a chance to see details spanning just 100 or so light-years — an impressive feat considering the galaxy lives in a universe just 1.8 billion years old. “This is exactly why gravitational lensing is so amazing!” says study coauthor Catherine Vlahakis (ALMA and European Southern Observatory, Chile).

Galaxy Collisions in the Early Universe Reconstructed map of SDP.81

This reconstruction shows SDP.81 without the distorting magnification provided by gravitational lensing. The colored map shows clumpy carbon monoxide emission at submillimeter wavelengths, with continuum submillimeter emission overlaid in white contours. The yellow contours show the placement of the blob of gas recovered from the Hubble image.
Simon Dye & others

As the initial results on SDP.81 were accepted for publication in the Astrophysical Journal, another team led by Simon Dye (Nottingham University, UK) reconstructed the lensed galaxy’s shape based on the distorted light that ALMA and Hubble imaged.

The reconstructed ALMA image shows a rotating disk of dusty gas. Oddly enough, the reconstructed Hubble image, which probes visible light rather than submillimeter-wavelength emission, shows something completely different — a blob of gas offset from the disk.

The disk and blob might be two distant galaxies coincidentally close together along the sky, the authors acknowledge. But just as likely for this crowded time period is that one galaxy has passed through another, leaving behind a dusty disk galaxy that’s popping with stars — about 500 Suns’ worth a year.

These types of merger-induced starburst galaxies were probably common in the early universe. Now with some of the highest-resolution observations to date, astronomers can study their makeup and learn about the earliest phases of galaxy evolution.

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