Into The Submillimeter: The Early Universe’s Formation

A new study looked at 52 submillimeter galaxies to help us understand the early ages of our Universe. Image: University of Nottingham/Omar Almaini
A new study looked at 52 submillimeter galaxies to help us understand the early ages of our Universe. Image: University of Nottingham/Omar Almaini

In order to make sense of our Universe, astronomers have to work hard, and they have to push observing technology to the limit. Some of that hard work revolves around what are called sub-millimeter galaxies (SMGs.) SMGs are galaxies that can only be observed in the submillimeter range of the electromagnetic spectrum.

The sub-millimeter range is the waveband between the far-infrared and microwave wavebands. (It’s also called Terahertz radiation.) We’ve only had the capability to observe in the sub-millimeter range for a couple decades. We’ve also increased the angular resolution of telescopes, which helps us discern separate objects.

The submillimter wavelength is also called Terahertz Radiation, and is between Infrared and Microwave Radiation on the spectrum. Image: By Tatoute, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6884073
The submillimter wavelength is also called Terahertz Radiation, and is between Infrared and Microwave Radiation on the spectrum. Image: By Tatoute, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6884073

SMGs themselves are dim in other wavelengths, because they’re obscured by dust. The optical light is blocked by the dust, and absorbed and re-emitted in the sub-millimeter range. In the sub-millimeter, SMGs are highly luminous; trillions of times more luminous than the Sun, in fact.

This is because they are extremely active star-forming regions. SMGs are forming stars at a rate hundreds of times greater than the Milky Way. They are also generally older, more distant galaxies, so they’re red-shifted. Studying them helps us understand galaxy and star formation in the early universe.

ALMA is an array of dishes located at the Atacama Desert in Chile. Image: ALMA (ESO/NAOJ/NRAO), O. Dessibourg

A new study, led by James Simpson of the University of Edinburgh and Durham University, has examined 52 of these galaxies. In the past, it was difficult to know the exact location of SMGs. In this study, the team relied on the power of the Atacama Large Millimeter/submillimeter array (ALMA) to get a much more precise measurement of their location. These 52 galaxies were first identified by the Submillimeter Common-User Bolometer Array (SCUBA-2) in the UKIDSS Ultra Deep Survey.

There are four major results of the study:

  1. 48 of the SMGs are non-lensed, meaning that there is no object of sufficient mass between us and them to distort their light. Of these, the team was able to constrain the red-shift (z) for 35 of them to a median range of z-2.65. When it comes to extra-galactic observations like this, the higher the red-shift, the further away the object is. (For comparison, the highest red-shift object we know of is a galaxy called GN-z11, at z=11.1, which corresponds to about 400 million years after the Big Bang.
  2. Another type of galaxy, the Ultra-Luminous Infrared Galaxy (ULIRG) were thought to be evolved versions of SMGs. But this study showed that SMGs are larger and cooler than ULIRGs, which means that any evolutionary link between the two is unlikely.
  3. The team calculated estimates of dust mass in these galaxies. Their estimates suggest that effectively all of the optical-to-near-infrared light from co-located stars is obscured by dust. They conclude that a common method in astronomy used to characterize astronomical light sources, called Spectral Energy Distribution (SED), may not be reliable when it comes to SMGs.
  4. The fourth result is related to the evolution of galaxies. According to their analysis, it seems unlikely that SMGs can evolve into spiral or lenticular galaxies (a lenticular galaxy is midway between a spiral and an elliptical galaxy.) Rather, it appears that SMGs are the progenitors of elliptical galaxies.
The Pinwheel Galaxy (M101, NGC 5457) is a stunning example of a spiral galaxy. This study determines that there likely is no evolutionary link between sub-millimeter galaxies and spiral galaxies. Image: European Space Agency & NASA. CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=36216331

This study was a pilot study that the team hopes to extend to many other SMGs in the future.

ALMA Captures Never-Before-Seen Details of Protoplanetary Disk

ALMA’s best image of a protoplanetary disk to date. This picture of the nearby young star TW Hydrae reveals the classic rings and gaps that signify planets are in formation in this system. Credit: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO)
ALMA’s best image of a protoplanetary disc to date. This picture of the nearby young star TW Hydrae reveals the classic rings and gaps that signify planets are in formation in this system.
ALMA’s best image of a protoplanetary disk to date. This picture of the nearby young star TW Hydrae reveals the classic rings and gaps that signify planets are in formation in this system. Credit: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO)

TW Hydrae is a special star. Located 175 light years from Earth in the constellation Hydra the Water Snake, it sits at the center of a dense disk of gas and dust that astronomers think resembles our solar system when it was just 10 million years old. The disk is incredibly clear in images made using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which employs 66 radio telescopes sensitive to light just beyond that of infrared.  Spread across more than 9 miles (15 kilometers), the ALMA array acts as a gigantic single telescope that can make images 10 times sharper than even the Hubble Space Telescope.

This photo of the ALMA antennas on the Chajnantor Plateau in Chile, more than 16,000 feet (5000 meters) above sea level, was taken a few days before the start of ALMA Early Science and shows only one cluster of the 66 dishes. ALMA views the sky in "submillimeter" light, a slice of the spectrum invisible to the human eye that lies between infrared and radio waves. Credit: ALMA (ESO/NAOJ/NRAO)/W. Garnier (ALMA)
This photo of the ALMA antennas on the Chajnantor Plateau in Chile, more than 16,000 feet (5000 meters) above sea level, was taken a few days before the start of ALMA Early Science and shows only one cluster of the 66 dishes. ALMA views the sky in submillimeter light, a slice of the spectrum invisible to the human eye that lies between infrared and radio waves. Credit: ALMA (ESO/NAOJ/NRAO)/W. Garnier (ALMA)

Astronomers everywhere point their telescopes at TW Hydrae because it’s the closest infant star in the sky. With an age of between 5 and 10 million years, it’s not even running on hydrogen fusion yet, the process by which stars convert hydrogen into helium to produce energy. TW Hydrae shines from the energy released as it contracts through gravity. Fusion and official stardom won’t begin until it’s dense enough and hot enough for fusion to fire up in its belly.

ALMA image of the planet-forming disk around the young, sun-like star TW Hydrae. The inset image (upper right) zooms in on the gap nearest to the star, which is at the same distance as the Earth is from the sun, and may show an infant version of our home planet emerging from the dust and gas. The additional concentric light and dark features represent other planet-forming regions farther out in the disk. Credit: S. Andrews (Harvard-Smithsonian CfA), ALMA (ESO/NAOJ/NRAO)
ALMA image of the planet-forming disk around the young, sun-like star TW Hydrae. The inset image (upper right) zooms in on the gap nearest to the star, which is at the same distance as the Earth is from the sun, and may show an infant version of our home planet emerging from the dust and gas. The additional concentric light and dark features represent other planet-forming regions farther out in the disk. Credit: S. Andrews (Harvard-Smithsonian CfA), ALMA (ESO/NAOJ/NRAO)

We see most protoplanetary disks at various angles, but TW’s has a face-on orientation as seen from Earth, giving astronomers a rare, undistorted view of the complete disk around the star. The new images show amazing detail, revealing a series of concentric bright rings of dust separated by dark gaps. There’s even indications that a planet with an Earth-like orbit has begun clearing an orbit.

“Previous studies with optical and radio telescopes confirm that TW Hydrae hosts a prominent disk with features that strongly suggest planets are beginning to coalesce,” said Sean Andrews with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, USA and lead author on a paper published today in the Astrophysical Journal Letters.

Blurry as it is, the detail here is staggering. It shows a gap about 93 million miles from the central starsuggesting that a planet with a similar orbit to Earth is forming there. Credit: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO)
The model (at left) of a protoplanetary disk shows a newly forming star at the center of a saucer-shaped dust cloud. At right, a close up of TW Hydrae taken by ALMA shows a gap about 93 million miles from the central star, suggesting that a planet with a similar orbit to Earth is forming there. Credit: (Left: L. Calcada). Right: S. Andrews (Harvard-Smithsonian CfA); B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO)

Pronounced gaps that show up in the photos above are located at 1.9 and 3.7 billion miles (3-6 billion kilometers) from the central star, similar to the average distances from the sun to Uranus and Pluto in the solar system. They too are likely to be the results of particles that came together to form planets, which then swept their orbits clear of dust and gas to sculpt the remaining material into well-defined bands. ALMA picks up the faint emission of submillimeter light emitted by dust grains in the disk, revealing details as small as 93 million miles (150 million kilometers) or the distance of Earth from the sun

This image compares the size of the solar system with HL Tauri and its surrounding protoplanetary disc. Although the star is much smaller than the Sun, the disc around HL Tauri stretches out to almost three times as far from the star as Neptune is from the Sun. Credit:ALMA (ESO/NAOJ/NRAO)
This image compares the size of the solar system with HL Tauri and its surrounding protoplanetary disc. Although the star is much smaller than the Sun, the disc around HL Tauri stretches out to almost three times as far from the star as Neptune is from the Sun. Credit:ALMA (ESO/NAOJ/NRAO)

“This is the highest spatial resolution image ever of a protoplanetary disk from ALMA, and that won’t be easily beaten in the future!” said Andrews.

Earlier ALMA observations of another system, HL Tauri, show that even younger protoplanetary disks — a mere 1 million years old — look remarkably similar.  By studying the older TW Hydrae disk, astronomers hope to better understand the evolution of our own planet and the prospects for similar systems throughout the Milky Way.

Weekly Space Hangout – June 26, 2015: Paul Sutter, CCAPP Visiting Fellow

Host: Fraser Cain (@fcain)

Special Guest: This week we welcome Paul Sutter, the CCAPP Visiting Fellow who works on the cosmic microwave background and large-scale structure.

Guests:
Jolene Creighton (@jolene723 / fromquarkstoquasars.com)
Brian Koberlein (@briankoberlein / briankoberlein.com)
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Alessondra Springmann (@sondy)
Continue reading “Weekly Space Hangout – June 26, 2015: Paul Sutter, CCAPP Visiting Fellow”

Distant Stellar Nurseries: This Time, in High Definition

The Milky Way glitters above the ALMA array in this image taken from a time lapse sequence during the ESO Ultra HD Expedition.

This article is a guest post by Anna Ho, who is currently doing research on stars in the Milky Way through a one-year Fulbright Scholarship at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany.

In the Milky Way, an average of seven new stars are born every year. In the distant galaxy GN20, an astonishing average of 1,850 new stars are born every year. “How,” you might ask, indignant on behalf of our galactic home, “does GN20 manage 1,850 new stars in the time it takes the Milky Way to pull off one?”

To answer this, we would ideally take a detailed look at the stellar nurseries in GN20, and a detailed look at the stellar nurseries in the Milky Way, and see what makes the former so much more productive than the latter.

But GN20 is simply too far away for a detailed look.

This galaxy is so distant that its light took twelve billion years to reach our telescopes. For reference, Earth itself is only 4.5 billion years old and the universe itself is thought to be about 14 billion years old. Since light takes time to travel, looking out across space means looking back across time, so GN20 is not only a distant, but also a very ancient, galaxy. And, until recently, astronomers’ vision of these distant, ancient galaxies has been blurry.

Consider what happens when you try to load a video with a slow Internet connection, or when you download a low-resolution picture and then stretch it. The image is pixelated. What was once a person’s face becomes a few squares: a couple of brown squares for hair, a couple of pink squares for the face. The low-definition picture makes it impossible to see details: the eyes, the nose, the facial expression.

A face has many details and a galaxy has many varied stellar nurseries. But poor resolution, a result simply of the fact that ancient galaxies like GN20 are separated from our telescopes by vast cosmic distances, has forced astronomers to blur together all of this rich information into a single point.

The situation is completely different here at home in the Milky Way. Astronomers have been able to peer deep into stellar nurseries and witness stellar birth in stunning detail. In 2006, the Hubble Space Telescope took this unprecedentedly detailed action shot of stellar birth at the heart of the Orion Nebula, one of the Milky Way’s most famous stellar nurseries:

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A detailed close-up of stellar birth. Credit: NASA,ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team

There are over 3,000 stars in this image: The glowing dots are newborn stars that have recently emerged from their cocoons. Stellar cocoons are made of gas: thousands of these gas cocoons sit nestled in immense cosmic nurseries, which are rich with gas and dust. The central region of that Hubble image, encased by what looks like a bubble, is so clear and bright because the massive stars within have blown away the dust and gas they were forged from. Majestic stellar nurseries are scattered all over the Milky Way, and astronomers have been very successful at uncloaking them in order to understand how stars are made.

Observing nurseries both here at home and in relatively nearby galaxies has enabled astronomers to make great leaps in understanding stellar birth in general: and, in particular, what makes one nursery, or one star formation region, “better” at building stars than another. The answer seems to be: how much gas there is in a particular region. More gas, faster rate of star birth. This relationship between the density of gas and the rate of stellar birth is called the Kennicutt-Schmidt Law. In 1959, the Dutch astronomer Maarten Schmidt raised the question of how exactly increasing gas density influences star birth, and forty years later, in an illustration of how scientific dialogues can span decades, his American colleague Robert Kennicutt used data from 97 galaxies to answer him.

Understanding the Kennicutt-Schmidt Law is crucial for determining how stars form and even how galaxies evolve. One fundamental question is whether there is one rule that governs all galaxies, or whether one rule governs our galactic neighborhood, but a different rule governs distant galaxies. In particular, a family of distant galaxies known as “starburst galaxies” seems to contain particularly productive nurseries. Dissecting these distant, highly efficient stellar factories would mean probing galaxies as they used to be, back near the beginning of the universe.

Enter GN20. GN20 is one of the brightest, most productive of these starburst galaxies. Previously a pixelated dot in astronomers’ images, GN20 has become an example of a transformation in technological capability.

In December 2014, an international team of astronomers led by Dr. Jacqueline Hodge of the National Radio Astronomy Observatory in the USA, and comprising astronomers from Germany, the United Kingdom, France, and Austria, were able to construct an unprecedentedly detailed picture of the stellar nurseries in GN20. Their results were published earlier this year.

The key is a technique called interferometry: observing one object with many telescopes, and combining the information from all the telescopes to construct one detailed image. Dr. Hodge’s team used some of the most sophisticated interferometers in the world: the Karl G. Jansky Very Large Array (VLA) in the New Mexico desert, and the Plateau de Bure Interferometer (PdBI) at 2550 meters (8370 feet) above sea level in the French Alps.

With data from these interferometers as well as the Hubble Space Telescope, they turned what used to be one dot into the following composite image:

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GN20 in unprecedented detail (false color image). The 10 kpc (10,000 parsec) scale corresponds to 32,600 light-years. Image credit: Jacqueline Hodge et al. 2015

This is a false color image, and each color stands for a different component of the galaxy. Blue is ultraviolet light, captured by the Hubble Space Telescope. Green is cold molecular gas, imaged by the VLA. And red is warm dust, heated by the star formation it is shrouding, detected by the PdBI.

Unbundling one pixel into many enabled the team to determine that the nurseries in a starburst galaxy like GN20 are fundamentally different from those in a “normal” galaxy like the Milky Way. Given the same amount of gas, GN20 can churn out orders of magnitude more stars than the Milky Way can. It doesn’t simply have more raw material: it is more efficient at fashioning stars out of it.

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Some of the 66 radio antennas of ALMA, which can be linked to act like a much larger telescope. Image credit: ALMA (ESO/NAOJ/NRAO)/B. Tafreshi (twanight.org)

This kind of study is currently unique to the extreme case of GN20. However, it will be more common with the new generation of interferometers, such as the Atacama Large Millimeter/submillimeter Array (ALMA).

Located 5000 meters (16000 feet) high up in the Chilean Andes, ALMA is poised to transform astronomers’ understanding of stellar birth. State-of-the-art telescopes are enabling astronomers to do the kind of detailed science with distant galaxies – ancient galaxies from the early universe – that was once thought to be possible only for our local neighborhood. This is crucial in the scientific quest for universal physical laws, as astronomers are able to test their theories beyond our neighborhood, out across space and back through time.

Weekly Space Hangout – April 17, 2015: Amy Shira Teitel and “Breaking the Chains of Gravity”

Host: Fraser Cain (@fcain)
Special Guest: Amy Shira Teitel (@astVintageSpace) discussing space history and her new book Breaking the Chains of Gravity
Guests:
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )

This Week’s Stories:
Falcon 9 launch and (almost!) landing
NASA Invites ESA to Build Europa Piggyback Probe
Bouncing Philae Reveals Comet is Not Magnetised
Astronomers Watch Starbirth in Real Time
SpaceX Conducts Tanking Test on In-Flight Abort Falcon 9
Rosetta Team Completely Rethinking Comet Close Encounter Strategy
Apollo 13 Custom LEGO Minifigures Mark Mission’s 45th Anniversary
LEGO Launching Awesome Spaceport Shuttle Sets in August
New Horizons Closes in on Pluto
Work Platform to be Installed in the Vehicle Assembly Building at NASA’s Kennedy Space Center in Florida.
Watching the Sunsets of Mars Through Robot Eyes: Photos
NASA Invites ESA to Build Europa Piggyback Probe
ULA Plans to Introduce New Rocket One Piece at a Time
Two Mysterious Bright Spots on Dwarf Planet Ceres Are Not Alike
18 Image Montage Show Off Comet 67/P Activity
ULA’s Next Rocket To Be Named Vulcan
NASA Posts Huge Library of Space Sounds And You’re Free to Use Them
Explaining the Great 2011 Saturn Storm
Liquid Salt Water May Exist on Mars
Color Map Suggests a Once-Active Ceres
Diverse Destinations Considered for New Interplanetary Probe
Paul Allen Asserts Rights to “Vulcan” Trademark, Challenging Name of New Rocket
First New Horizons Color Picture of Pluto and Charon
NASA’s Spitzer Spots Planet Deep Within Our Galaxy
Icy Tendrils Reaching into Saturn Ring Traced to Their Source
First Signs of Self-Interacting Dark Matter?
Anomaly Delays Launch of THOR 7 and SICRAL 2
Nearby Exoplanet’s Hellish Atmosphere Measured
The Universe Isn’t Accelerating As Fast As We Thought
Glitter Cloud May Serve As Space Mirror
Cassini Spots the Sombrero Galaxy from Saturn
EM-1 Orion Crew Module Set for First Weld Milestone in May
Special Delivery: NASA Marshall Receives 3D-Printed Tools from Space
The Roomba for Lawns is Really Pissing Off Astronomers
Giant Galaxies Die from the Inside Out
ALMA Reveals Intense Magnetic Field Close to Supermassive Black Hole
Dawn Glimpses Ceres’ North Pole
Lapcat A2 Concept Sup-Orbital Spaceplane SABRE Engine Passed Feasibility Test by USAF Research Lab
50 Years Since the First Full Saturn V Test Fire
ULA CEO Outlines BE-4 Engine Reuse Economic Case
Certification Process Begins for Vulcan to Carry Military Payloads
Major Advance in Artificial Photosynthesis Poses Win/Win for the Environment
45th Anniversary [TODAY] of Apollo 13’s Safe Return to Earth
Hubble’s Having A Party in Washington Next Week (25th Anniversary of Hubble)

Don’t forget, the Cosmoquest Hangoutathon is coming soon!

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Google+, Universe Today, or the Universe Today YouTube page.

You can join in the discussion between episodes over at our Weekly Space Hangout Crew group in G+, and suggest your ideas for stories we can discuss each week!

Pluto-like Objects Turn to Dust Around a Nearby Young Star

ALMA image of the dust surrounding the star HD 107146. Dust in the outer reaches of the disk is thicker than in the inner regions, suggesting that a swarm of Pluto-size planetesimals is causing smaller objects to smash together. The dark ring-like structure in the middle portion of the disk may be evidence of a gap where a planet is sweeping its orbit clear of dust. Credit: L. Ricci ALMA (NRAO/NAOJ/ESO); B. Saxton (NRAO/AUI/NSF)

A planetary system’s early days readily tell of turmoil. Giant planets are swept from distant birthplaces into sizzling orbits close to their host star. Others are blasted away from their star into the darkness of space. And smaller bodies, like asteroids and comets, are being traded around constantly.

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have seen the latter: swarms of Pluto-size objects turning to dust around a young star. And the image is remarkable.

“This system offers us the chance to study an intriguing time around a young, Sun-like star,” said coauthor Stuartt Corder and ALMA Deputy Director in a news release. “We are possibly looking back in time here, back to when the Sun was about 2 percent of its current age.”

The young star, HD 107146, is located roughly 90 light-years from Earth in the direction of the constellation Coma Berenices. Although the star itself is visible in any small telescope, ALMA can probe the star’s radically faint protoplanetary disk. This is the star’s dusty cocoon that coalesces into planets, comets and asteroids.

ALMA’s image revealed an unexpected bump in the number of millimeter-size dust grains far from the host star. This highly concentrated band spans roughly 30 to 150 astronomical units, the equivalent of Neptune’s orbit around the Sun to four times Pluto’s orbit.

So where is the extra dust coming from?

Typically, dust in the debris disk is simply left over material from the formation of planets. Early on, however, Pluto-size objects (otherwise known as planetesimals) will collide and blast themselves apart, also contributing to the dust. Certain models predict that this leads to a much higher concentration of dust in the most distant regions of the disk.

Although this is the case for HD 107146, “this is the opposite of what we see in younger primordial disks where the dust is denser near the star,” said lead author Luca Ricci from the Harvard-Smithsonian Center for Astrophysics. “It is possible that we caught this particular debris disk at a stage in which Pluto-size planetesimals are forming right now in the outer disk while other Pluto-size bodies have already formed closer to the star.”

Adding to this hypothesis is the fact that there’s a slight depression in the dust at 80 astronomical units, or twice Pluto’s average distance from the Sun. This could be a slight gap in the dust, where an Earth-size planet is sweeping the area clear of a debris disk.

If true, this would be the first observation of an Earth-size planet forming so far from its host star. But for now that’s a big if.

The results will be published in the Astrophysical Journal and are available online.