Cosmic Void Contains Fewer Galaxies than Expected, which, Ironically, Makes it Harder for Light to get Through

According to the Big Bang Theory of cosmology, the Universe began roughly 13.8 billion years ago as all matter in the Universe began to expand from a single point of infinite density. Over the next few billion years, the fundamental forces of the Universe began to separate from each other and subatomic particles and atoms formed. In time, this first stars and galaxies formed, giving rise to the large-scale structure of the Universe.

However, it was only by roughly 1 billion years after the Big Bang that the Universe began to become transparent. By about 12 billion years ago, intergalactic space was filled with gas that was much less transparent than it is now, with variations from place to place. To address why this was, a team of astronomers recently used the world’s largest telescope to search for galaxies of young stars in a huge volume of space.

The study which details their findings recently appeared in The Astrophysical Journal under the title “Evidence for Large-scale Fluctuations in the Metagalactic Ionizing Background Near Redshift Six“. The study was led by George D. Becker, a professor of astrophysics at the University of California Riverside, and included members from the University of California, Los Angeles (UCLA), and the University of California, Santa Barbara (UCSB).

This illustration shows the evolution of the Universe, from the Big Bang on the left, to modern times on the right. Credit: NASA

For the sake of their study, the team used the Subaru Telescope – the world’s largest telescope, located at the Mauna Kea Observatories in Hawaii – to examine a 500 million light-year volume of space as it existed roughly 12 billion years ago. Using this data, the team considered two possible models that could account for the variations in transparency that astronomers have been seeing during this cosmic epoch.

On the one hand, if the region contained a small number of galaxies, the team would conclude that startlight could not penetrate very far through the intergalactic gas. On the other hand, if it contained an unusually large number of galaxies, this would indicate that the region had cooled significantly over the previous several hundred million years. Prior to their observations, Beck and his team were expecting to find that it was the latter.

However, what they found was that the region contained far fewer galaxies than expected – which indicated that the opaqueness of the region was due to a lack of starlight. As Steven Furlanetto, a UCLA professor of astronomy and a co-author of the research, explained in a recent UCLA press release:

“It was a rare case in astronomy where two competing models, both of which were compelling in their own way, offered precisely opposite predictions, and we were lucky that those predictions were testable… It is not that the opacity is a cause of the lack of galaxies. Instead, it’s the other way around.”

In addition to addressing an enduring mystery in astronomy, this study also has implications for our understanding of how the Universe evolved over time. According to our current cosmological models, the period that took place roughly 380,000 t0 150 million years after the Big Bang is known as the “Dark Ages”. Most of the photons in the Universe were interacting with electrons and protons at this time, which means radiation from this period is undetectable by our current instruments.

However, by about 1 billion years after the Big Bang, the first stars and galaxies had formed. It is further believed that ultraviolet light from these first galaxies filled the Universe and is what allowed for the gas in deep space to become transparent. This would have occurred earlier in regions with more galaxies, the astronomers concluded, hence why there are variations in transparency.

In short, if more ultraviolet radiation from galaxies would lead to greater transparency in the early Universe, then the existence of fewer nearby galaxies would cause certain regions to be murkier. In the future, Becker and his team hope to further study this region of space and others like it in the hope that it will reveal clues about how the first galaxies illuminated the Universe during that early period, which remains a subject of inquiry at this point.

This research is also expected to shed more light on how the early Universe evolved, gradually giving rise to the one that are familiar with today. And as next-generation instruments are able to probe deeper into space (and hence, further back in time), we just may come to understand how existence as we know it all unfolded.

Further Reading: UCLA, The Astrophysical Journal

Galaxies Swell due to Explosive Action of New Stars

In 1926, famed astronomer Edwin Hubble developed his morphological classification scheme for galaxies. This method divided galaxies into three basic groups – Elliptical, Spiral and Lenticular – based on their shapes. Since then, astronomers have devoted considerable time and effort in an attempt to determine how galaxies have evolved over the course of billions of years to become these shapes.

One of th most widely-accepted theories is that galaxies changed by merging, where smaller clouds of stars – bound by mutual gravity – came together, altering the size and shape of a galaxy over time. However, a new study by an international team of researchers has revealed that galaxies could actually assumed their modern shapes through the formation of new stars within their centers.

The study, titled “Rotating Starburst Cores in Massive Galaxies at z = 2.5“, was recently published in the Astrophysical Journal Letters. Led by Ken-ichi Tadaki – a postdoctoral researcher with the Max Planck Institute for Extraterrestrial Physics and the National Astronomical Observatory of Japan (NAOJ) – the team conducted observations of distant galaxies in order to get a better understanding of galactic metamorphosis.

Evolution diagram of a galaxy. First the galaxy is dominated by the disk component (left) but active star formation occurs in the huge dust and gas cloud at the center of the galaxy (center). Then the galaxy is dominated by the stellar bulge and becomes an elliptical (or lenticular) galaxy. Credit: NAOJ

This involved using ground-based telescopes to study 25 galaxies that were at a distance of about 11 billion light-years from Earth. At this distance, the team was seeing what these galaxies looked like 11 billion years ago, or roughly 3 billion years after the Big Bang. This early epoch coincides with a period of peak galaxy formation in the Universe, when the foundations of most galaxies were being formed. As Dr. Tadaki indicated in a NAOJ press release:

“Massive elliptical galaxies are believed to be formed from collisions of disk galaxies. But, it is uncertain whether all the elliptical galaxies have experienced galaxy collision. There may be an alternative path.”

Capturing the faint light of these distant galaxies was no easy task and the team needed three ground-based telescopes to resolve them properly. They began by using the NAOJ’s 8.2-m Subaru Telescope in Hawaii to pick out the 25 galaxies in this epoch. Then they targeted them for observations with the NASA/ESA Hubble Space Telescope (HST) and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

Whereas the HST captured light from stars to discern the shape of the galaxies (as they existed 11 billion years ago), the ALMA array observed submillimeter waves  emitted by the cold clouds of dust and gas – where new stars are being formed. By combining the two, they were able to complete a detailed picture of how these galaxies looked 11 billion years ago when their shapes were still evolving.

Observation images of a galaxy 11 billion light-years away. Credit: ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, Tadaki et al.

What they found was rather telling. The HST images indicated that early galaxies were dominated by a disk component, as opposed to the central bulge feature we’ve come to associate with spiral and lenticular galaxies. Meanwhile, the ALMA images showed that there were massive reservoirs of gas and dust near the centers of these galaxies, which coincided with a very high rate of star formation.

To rule out alternate possibility that this intense star formation was being caused by mergers, the team also used data from the European Southern Observatory’s Very Large Telescope (VLT) – located at the Paranal Observatory in Chile – to confirm that there were no indications of massive galaxy collisions taking place at the time. As Dr. Tadaki explained:

“Here, we obtained firm evidence that dense galactic cores can be formed without galaxy collisions. They can also be formed by intense star formation in the heart of the galaxy.”

These findings could lead astronomers to rethink their current theories about galactic evolution and howthey came to adopt features like a central bulge and spiral arms. It could also lead to a rethink of our models regarding cosmic evolution, not to mention the history of own galaxy. Who knows? It might even cause astronomers to rethink what might happen in a few billion years, when the Milky Way is set to collide with the Andromeda Galaxy.

As always, the further we probe into the Universe, the more it reveals. With every revelation that does not fit our expectations, our hypotheses are forced to undergo revision.

Further Reading: ALMAAstrophysical Journal Letters

The Race To Image Exoplanets Heats Up!

Thanks to the deployment of the Kepler mission, thousands of extrasolar planet candidates have been discovered. Using a variety of indirect detection methods, astronomers have detected countless gas giants, super Earths, and other assorted bodies orbiting distant stars. And one terrestrial planet (Proxima b) has even been found lurking in the closest star system to Earth – Proxima Centauri.

The next step, quite logically, is to observe these planets directly. Hence why the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument was commissioned at the National Astronomical Observatory of Japan (NAOJ) in  Mauna Kea, Hawaii. Designed to allow for the direct detection of planets around other stars, this instrument will help ensure that the Subaru Telescope remains on the cutting-edge of exoplanet hunting.

As of January 22nd, 2017, some 3,565 exoplanet candidates have been detected in 2,675 planetary systems, and over 2000 of these have been confirmed. However, as already noted, the vast majority of these have been detected by  indirect means – generally through the measurement of a star’s radial velocity, or by measuring dips in a star’s luminosity as an exoplanet passes in front of it (i.e. the transit method).

The Subaru Telescope atop Mauna Kea. CHARIS works in conjunction with Subaru. Image: Dr. Hideaki Fujiwara - Subaru Telescope, NAOJ.
The Subaru Telescope atop Mauna Kea. CHARIS works in conjunction with Subaru. Credit: Dr. Hideaki Fujiwara/NAOJ

Adaptive Optics, meanwhile, have allowed for the detection of exoplanets directly. When used in astronomy, this technology removes the the effects of atmospheric interference so that light from distant stars or planets can be seen clearly. Relying on experimental technology, the SCExAO was specifically designed and optimized for imaging planets, and is one of several newly-commissioned extreme AO instruments.

However, as Dr. Thayne Currie – a research associate at the NOAJ – indicated, the Observatories on Mauna Kea are particularly well suited to the technology. “Mauna Kea is the best place on this planet to see planets in other stellar systems,” he said. “Now, we finally have an instrument designed to utilize this mountain’s special gifts and the results are breathtaking.”

What makes the SCExAO special is that it allows astronomers the ability to image planets with masses and orbital separations that are similar to those in our own Solar System. So far, about a dozen planets have been detected directly using AO instruments, but these planets have all been gas giants with 4 to 13 times the mass of Jupiter, and which orbit their stars at distances beyond that of Neptune from our Sun.

This improved imaging capacity is made possible by the SCExAO’s ability to compensate for atmospheric interference at a faster rate. This will enable the Subaru Telescope to be able to capture far images of distant stars that are sharper and subject to less glare. And astronomers will be able to discern the presence of fainter objects that are circling these stars – i.e. exoplanets – with greater ease.

The debris disk detected around a young star HD 36546 using SCExAO/HiCIAO (left, seen nearly edge-on) and its model (right, viewed face-on). Credit: NAOJ

The first discovery made with the SCExAO, took place back in October of 2016. At the time, the Subaru telescope had detected a debris disk around HD 36546 – a 2 solar-mass star in the direction of the Taurus constellation – which appeared almost edge on. Located about twice as far from HD 36546 as the Kuiper Belt is from our Sun, this disk is believed to be the youngest debris disk ever observed (3 to 10 million years old).

This test of the SCExAO not only revealed a disk that could be critical to studying the earliest stages of icy planet formation, but demonstrated the extreme sensitivity of the technology. Basically, it allowed the astronomers conducting the study to rule out the existence of any planets in the system, thus concluding that planetary dynamics played no role in sculpting the disk.

More recently, the SCExAO instrument managed to directly detect multiple planets in the system known as HR 8799, which it observed in July of 2016. Prior to this, some of the systems four planets were spotted by surveys conducted using the Keck and the Subaru telescope (before the SCExAO was incorporated). However, these surveys could not correct for all the glare coming from HR 8799, and could only image two of three of the planets as a result.

A follow-up was conducted in the Fall of 2016, combining data from the SCExAO with that obtained by the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS). This resulted in even clearer detection of the system’s inner three planets, not to mention high-quality spectrographic data that could allow researchers to determine the chemical compositions of their atmospheres.

The star and multiple planet system HR 8799 imaged using the SCEAO and the HiCIAO camera (left) and the Keck facility AO system coupled with the NIRC2 camera (right). Credit: NAOJ

As Dr. Olivier Guyon, the head of the SCExAO project, explained, this is a major improvement over other AO surveys. It also presents some major advantages when it comes to exoplanet hunting. “With SCExAO, we know not only the presence of a planet but also its character such as whether it is cloudy and what molecules it has, even if that planet is tens of trillions of miles away.”

Looking at the year ahead, the SCExAO is scheduled to undergo improvements that will allow it to detect planets that are 10 to 10o times fainter than what it can right now. The CHARIS instrument is also scheduled for additional engineering tests to improve its capabilities. These improvements are also expected to be incorporated into next-generation telescopes like the Thirty Meter Telescope – which is currently under construction at Mauna Kea.

Other recently-commissioned extreme AO instruments include the Gemini Planet Imager (GPI) at Gemini Observatory on its telescope in Chile, the Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) on Very Large Telescope (VLT) in Chile, and the AO system on the Large Binocular Telescope (LBT) in Arizona. And these are only some of the current attempts to reduce interference and make exoplanets easier to detect.

For instance, coronagraph are another way astronomers are attempting to refine their search efforts. Consisting of tiny instruments that are fitted inside telescopes, coronagraphs block the incoming light of a star, thus enabling telescopes to spot the faint light being reflected from orbiting planets. When paired with spectrometers, scientists are able to conduct studies of these planet’s atmospheres.

An artist's illustration of the Starshade deployed near its companion telescope. Image: NASA
An artist’s illustration of the Starshade deployed near its companion space telescope. Credit: NASA

And then you have more ambitious projects like Starshade, a concept currently being developed by Northrop Grumman with the support of NASA’s Jet Propulsion Laboratory. This concept calls for a giant, flower-shaped screen that would be launched with one of NASA’s next-generation space telescopes. Once deployed, it would fly around in front of the telescope in order to obscure the light coming from distant stars.

The era of exoplanet discovery loometh! In the coming decades, we are likely to see an explosion in the number of planets were are able to observe directly. And in so doing, we can expect the number of potentially habitable exoplanets to grow accordingly.

Further Reading: NAOJ/Subaru Telescope

Japanese 3D Galaxy Map Confirms Einstein Was One Smart Dude

On June 30th, 1905, Albert Einstein started a revolution with the publication of theory of Special Relativity. This theory, among other things, stated that the speed of light in a vacuum is the same for all observers, regardless of the source. In 1915, he followed this up with the publication of his theory of General Relativity, which asserted that gravity has a warping effect on space-time. For over a century, these theories have been an essential tool in astrophysics, explaining the behavior of the Universe on the large scale.

However, since the 1990s, astronomers have been aware of the fact that the Universe is expanding at an accelerated rate. In an effort to explain the mechanics behind this, suggestions have ranged from the possible existence of an invisible energy (i.e. Dark Energy) to the possibility that Einstein’s field equations of General Relativity could be breaking down. But thanks to the recent work of an international research team, it is now known that Einstein had it right all along.

Continue reading “Japanese 3D Galaxy Map Confirms Einstein Was One Smart Dude”

Supermassive Black Holes In Distant Galaxies Are Mysteriously Aligned

A supermassive black hole has been found in an unusual spot: an isolated region of space where only small, dim galaxies reside. Image credit: NASA/JPL-Caltech

In 1974, astronomers detected a massive source of radio wave emissions coming from the center of our galaxy. Within a few decades time, it was concluded that the radio wave source corresponded to a particularly large, spinning black hole. Known as Sagittarius A, this particular black hole is so large that only the designation “supermassive” would do. Since its discovery, astronomers have come to conclude that supermassive black holes (SMBHs) lie at the center of almost all of the known massive galaxies.

But thanks to a recent radio imaging by a team of researchers from the University of Cape Town and University of the Western Cape, in South Africa, it has been further determined that in a region of the distant universe, the SMBHs are all spinning out radio jets in the same direction. This finding, which shows an alignment of the jets of galaxies over a large volume of space, is the first of its kind, and could tell us much about the early Universe.

Continue reading “Supermassive Black Holes In Distant Galaxies Are Mysteriously Aligned”

The Early Universe Was All About Galactic Hook Ups

In about 4 billion years, scientists estimate that the Andromeda and the Milky Way galaxies are expected to collide, based on data from the Hubble Space Telescope. And when they merge, they will give rise to a super-galaxy that some are already calling Milkomeda or Milkdromeda (I know, awful isn’t it?) While this may sound like a cataclysmic event, these sorts of galactic collisions are quite common on a cosmic timescale.

As an international group of researchers from Japan and California have found, galactic “hookups” were quite common during the early universe. Using data from the Hubble Space Telescope and the Subaru Telescope at in Mauna Kea, Hawaii, they have discovered that 1.2 billion years after the Big Bang, galactic clumps grew to become large galaxies by merging. As part of the Hubble Space Telescope (HST) “Cosmic Evolution Survey (COSMOS)”, this information could tell us a great about the formation of the early universe.

Continue reading “The Early Universe Was All About Galactic Hook Ups”

Subaru Telescope Spots Galaxies From The Early Universe

The expansion of the universe over most of its history has been relatively gradual. The notion that a rapid period "inflation" preceded the Big Bang expansion was first put forth 25 years ago. The new WMAP observations favor specific inflation scenarios over other long held ideas.

It’s an amazing thing, staring into deep space with the help of a high-powered telescope. In addition to being able to through the vast reaches of space, one is also able to effectively see through time.

Using the Subaru Telescope’s Suprime-Cam, a team of astronomers has done just that. In short, they looked back 13 billion years and discovered 7 early galaxies that appeared quite suddenly within 700 million years of the Big Bang. In so doing, they discovered clues to one of astronomy’s most burning questions: when and how early galaxies formed in our universe.

The team, led by graduate student Akira Konno and Dr. Masami Ouchi (Associate Professor at the University of Tokyo’s ICRR) was looking for a specific kind of galaxy called a Lyman-alpha emitter (LAE), to understand the role such galaxies may have played in an event called “cosmic reionization”.

The current cosmological model states that the universe was born in the Big Bang some 13.8 billion years ago. In its earliest epochs, it was filled with a hot “soup” of charged protons and electrons. As the newborn universe expanded, its temperature decreased uniformly.

 Credit: NASA, ESA & A. Felid (STScI)).
It is estimated that the first stars and galaxies formed 12.8 billion years ago, during a period of “cosmic reionization”. Credit: NASA/ESA/A. Felid (STScI)

When the universe was 400,000 years old, conditions were cool enough to allow the protons and electrons to bond and form neutral hydrogen atoms. That event is called “recombination” and resulted in a universe filled with a “fog” of these neutral atoms.

Eventually the first stars and galaxies began to form, and their ultraviolet light ionized the hydrogen atoms, and “divided” the neutral hydrogen into protons and electrons again. As this occurred, the “fog” of neutral hydrogen cleared.

Astronomers call this event “cosmic reionization” and think that it ended about 12.8 billion years ago – a billion years after the Big Bang. The timing of this event – when it started and how long it lasted – is one of the big questions in astronomy.

To investigate this cosmic reionization, the Subaru team searched for early LAE galaxies at a distance of 13.1 billion light years. Although Hubble Space Telescope has found more distant LAE galaxies, the discovery of seven such galaxies at 13.1 billion light-years represents a distance milestone for Subaru Telescope.

Color composite images of seven LAEs found in this study as they appeared 13.1 billion years ago. This represents the combination of three filter images from Subaru Telescope. Red objects between two white lines are the LAEs. The LAEs of 13.1 billion years ago have a quite red color due to the effects of cosmic expansion on their component wavelengths of light. Credit: ICRR, University of Tokyo
Color composite images of seven LAEs found in the study. The red objects between two white lines are the LAEs. Credit: ICRR, University of Tokyo

Mr. Konno, the graduate student heading the analysis of the data from the Subaru Telescope pointed out the obstacles that Subaru had to overcome to make the observations.”It is quite difficult to find the most distant galaxies due to the faintness of the galaxies.” he said. “So, we developed a special filter to be able to find a lot of faint LAEs. We loaded the filter onto Suprime-Cam and conducted the most distant LAE survey with the integration time of 106 hours.”

That extremely long integration time was one of the longest ever performed at Subaru Telescope. It allowed for unprecedented sensitivity and enabled the team to search for as many of the most distant LAEs as possible.

According to Konno, the team expected to find several tens of LAEs. Instead they only found seven.

“At first we were very disappointed at this small number,” Konno said. “But we realized that this indicates LAEs appeared suddenly about 13 billion years ago. This is an exciting discovery. We can see that the luminosities suddenly brightened during the 700-800 million years after the Big Bang. What would cause this?”

Figure 2: This shows evolution of the Lyman-alpha luminosities of the galaxies. The yellow circle at 1 billion years after the Big Bang is used for normalization. The yellow circles come from previous studies, and the yellow dashed line shows the expected evolutionary trend of the luminosity. The current finding is shown by a red circle, and we can see that the galaxies appear suddenly when the universe was 700 million years old. This indicates that the neutral hydrogen fog was suddenly cleared, allowing the galaxies to shine out, as indicated by the backdrop shown for scale and illustration. Credit: ICRR, University of Tokyo; Hubble Space Telescope/NASA/ESA
This shows evolution of the Lyman-alpha luminosities of the galaxies. Credit: ICRR, University of Tokyo; Hubble Space Telescope/NASA/ESA

As the table above illustrates, the luminosities of LAEs changed based on this study. The yellow circle at 1 billion years after the Big Bang is used for normalization. The yellow circles come from previous studies, and the yellow dashed line shows the expected evolutionary trend of the luminosity.

The current finding is shown by a red circle, and we can see that the galaxies appear suddenly when the universe was 700 million years old. This indicates that the neutral hydrogen fog was suddenly cleared, allowing the galaxies to shine out, as indicated by the backdrop shown for scale and illustration.

According to the team’s analysis, one reason that LAEs appeared very quickly is cosmic reionization. LAEs in the epoch of cosmic reionization became darker than the actual luminosity due to the presence of the neutral hydrogen fog.

In the team’s analysis of their observations, they suggest the possibility that the neutral fog filling the universe was cleared about 13.0 billion years ago and LAEs suddenly appeared in sight for the first time.

“However, there are other possibilities to explain why LAEs appeared suddenly,” said Dr. Ouchi, who is the principal investigator of this program. “One is that clumps of neutral hydrogen around LAEs disappeared. Another is that LAEs became intrinsically bright. The reason of the intrinsic brightening is that the Lyman-alpha emission is not efficiently produced by the ionized clouds in a LAE due to the significant escape of ionizing photons from the galaxy. In either case, our discovery is an important key to understanding cosmic reionization and the properties of the LAEs in early universe.”

Dr. Masanori Iye, who is a representative of the Thirty Meter Telescope (TMT) project of Japan, commented on the observations and analysis. “To investigate which possibility is correct, we will observe with HSC (Hyper Suprime-Cam) on Subaru Telescope, which has a field of view 7 times wider than Suprime-Cam, and TMT currently being built on the summit of Mauna Kea in Hawaii in the future. By these observations, we will clarify the mystery of how galaxies were born and cosmic reionization occurred.”

Further Reading: Subaru Telescope

Comet ISON Hosted A Rare Kind Of Nitrogen, Hinting At Reservoirs In Young Solar System

Comet ISON — that bright comet last year that broke up around Thanksgiving weekend — included two forms of nitrogen in its icy body, according to newly released observations from the Subaru Telescope.

Of the two types found, the discovery of isotope 15NH2 was the first time it’s ever been seen in a comet. Further, the observations from the Japanese team of astronomers show “there were two distinct reservoirs of nitrogen [in] the massive, dense cloud … from which our Solar System may have formed and evolved,” stated the National Astronomical Observatory of Japan.

Besides being pretty objects to look at, comets are considered valuable astronomical objects because they’re a sort of time capsule of conditions early in the universe. The “fresh” comets are believed to come from a vast area of icy bodies called the Oort Cloud, a spot that has been relatively untouched since the solar system formed about 4.6 billion years ago. Spying elements inside of comets can give clues as to what was present in our neighborhood when the sun and planets were just coming to be.

“Ammonia (NH3) is a particularly important molecule, because it is the most abundant nitrogen-bearing volatile (a substance that vaporizes) in cometary ice and one of the simplest molecules in an amino group (–NH2) closely related to life. This means that these different forms of nitrogen could link the components of interstellar space to life on Earth as we know it,” NAOJ stated.

You can read more details about the finding at the NAOJ website, or in Astrophysical Journal Letters.

Greedy Galaxies Gobbled Gas, Stalling Star Formation Billions Of Years Ago

Like millionaires that burn through their cash too quickly, astronomers have found one factor behind why compact elliptical galaxies stopped growing stars about 11 billion years ago: they ate through their gas reserves.

The revelation comes as researchers released a new evolutionary track for compact elliptical galaxies that stopped their star formation when the universe was just three billion years old. When these galaxies ran out of gas, some of them cannibalized smaller galaxies to create giant elliptical galaxies. The “burned-out”galaxies have stars crowding 10 to 100 times more densely than elliptical galaxies formed more recently through a different evolutionary track.

“We at last show how these compact galaxies can form, how it happened, and when it happened. This basically is the missing piece in the understanding of how the most massive galaxies formed, and how they evolved into the giant ellipticals of today,” stated Sune Toft, who led the study and is a researcher at the Dark Cosmology Center at the Niels Bohr Institute in Copenhagen.

“This had been a great mystery for many years, because just three billion years after the Big Bang we see that half of the most massive galaxies have already completed their star formation.”

How massive elliptical galaxies evolved in about 13 billion years. Credit: NASA, ESA, S. Toft (Niels Bohr Institute), and A. Feild (STScI)
How massive elliptical galaxies evolved in about 13 billion years. Credit: NASA, ESA, S. Toft (Niels Bohr Institute), and A. Feild (STScI)

The team got a snapshot of these galaxies’ evolution by looking at a representative sample with the Hubble Space Telescope, specifically through the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) and a spectroscopic survey called 3D-HST. To find out how old the stars were, they combined the Hubble work with data gathered from the  Spitzer Space Telescope and the Subaru Telescope in Hawaii.

Next, they examined ancient, fast-star-forming submillimeter galaxies with data gathered from a range of space and ground-based telescopes.

The Hubble Space Telescope. image credit: NASA, tweaked by D. Majaess.
The Hubble Space Telescope. image credit: NASA, tweaked by D. Majaess.

“This multi-spectral information, stretching from optical light through submillimeter wavelengths, yielded a full suite of information about the sizes, stellar masses, star-formation rates, dust content, and precise distances of the dust-enshrouded galaxies that were present early in the universe,” Hubble’s news center stated.

The group found that that the submillimeter galaxies were likely “progenitors” of compact elliptical galaxies, as they share predicted characteristics of the ancestors. Further, researchers calculated that starbursts in submillimeter galaxies only went on for about 40 million years before the galaxies ran out of gas.

You can read the results in the Feb. 20 edition of the Astrophysical Journal or in prepublished version in Arxiv.

Source: Hubble News Center

What Fuels The Engine Of A Supermassive Black Hole?

If you could get a good look at the environment around a supermassive black hole — which is a black hole often found in the center of the galaxy — what factors would make that black hole keep going?

A Japanese study revealed that at least one of these black holes stay “active and luminous” by gobbling up nearby material, but notes that only a few of the observed galaxies that are merging have these types of black holes. This must mean something unique arises in the environment near the black hole to get it going, the researchers say. What that is, though, is still poorly understood.

Supermassive black holes, defined as black holes that have a million times the mass of the sun or more, reside in galaxy centers. “The merger of gas-rich galaxies with SMBHs [supermassive black holes] in their centers not only causes active star formation, but also stimulates mass accretion onto the existing SMBHs,” stated a press release from the Subaru Telescope.

“When material accretes onto a SMBH, the accretion disk surrounding the black hole becomes very hot from the release of gravitational energy, and it becomes very luminous. This process is referred to as active galactic nucleus (AGN) activity; it is different from the energy generation activity by nuclear fusion reactions within stars.”

Figuring out how these types of activity vary would give a clue as to how galaxies come together, the researchers said, but it’s hard to see anything in action because of dust and gas blocking the view of optical telescopes. That’s why infrared observations come in so handy, because it makes it easier to peer through the debris. (You can see some examples from this research below.)

Examples of infrared K-band images of luminous, gas-rich, merging galaxies. Credit: NAOJ
Examples of infrared K-band images of luminous, gas-rich, merging galaxies. Credit: NAOJ

The team (led by the  National Astronomical Observatory of Japan’s Masatoshi Imanishi) used NAOJ’s Subaru’s Infrared Camera and Spectrograph (IRCS) and the telescope’s adaptive optics system in two bands of infrared. Researchers looked at 29 luminous gas-rich merging galaxies in the infrared and found “at least” one active supermassive black hole in all but one of the ones studied.  However, only four of these galaxies merging had multiple, active black holes.

“The team’s results mean that not all SMBHs in gas-rich merging galaxies are actively mass accreting, and that multiple SMBHs may have considerably different mass accretion rates onto SMBHs,” Subaru stated.

The implication is more about the environment around a supermassive black hole must be understood to figure out how mass accretes. Knowing more about this will improve computer simulations of galaxy mergers, the researchers said.

You can read the published study in the Astrophysical Journal or in prepublished form on Arxiv.

Source: Subaru Telescope