Astronomers use a Galaxy Cluster as an Extremely Powerful “Natural Telescope” to Peer Even Farther into the Universe

This illustration shows how gravitational lensing works. The gravity of a large galaxy cluster is so strong, it bends, brightens and distorts the light of distant galaxies behind it. The scale has been greatly exaggerated; in reality, the distant galaxy is much further away and much smaller. Credit: NASA, ESA, L. Calcada

When it comes to studying some of the most distant and oldest galaxies in the Universe, a number of challenges present themselves. In addition to being billions of light years away, these galaxies are often too faint to see clearly. Luckily, astronomers have come to rely on a technique known as Gravitational Lensing, where the gravitational force of a large object (like a galactic cluster) is used to enhance the light of these fainter galaxies.

Using this technique, an international team of astronomers recently discovered a distant and quiet galaxy that would have otherwise gone unnoticed. Led by researchers from the University of Hawaii at Manoa, the team used the Hubble Space Telescope to conduct the most extreme case of gravitational lensing to date, which allowed them to observe the faint galaxy known as eMACSJ1341-QG-1.

The study that describes their findings recently appeared in The Astrophysical Journal Letters under the title “Thirty-fold: Extreme Gravitational Lensing of a Quiescent Galaxy at z = 1.6″. Led by Harald Ebeling, an astronomer from the University of Hawaii at Manoa, the team included members from the Niels Bohr Institute, the Centre Nationale de Recherche Scientifique (CNRS), the Space Telescope Science Institute, and the European Southern Observatory (ESO).

The quiescent galaxy eMACSJ1341-QG-1 as seen by the Hubble Space Telescope. The yellow dotted line traces the boundaries of the galaxy’s gravitationally lensed image. The inset on the upper left shows what eMACSJ1341-QG-1 would look like if we observed it directly, without the cluster lens. Credit: Harald Ebeling/UH IfA

For the sake of their study, the team relied on the massive galaxy cluster known as eMACSJ1341.9-2441 to magnify the light coming from eMACSJ1341-QG-1, a distant and fainter galaxy. In astronomical terms, this galaxy is an example of a “quiescent galaxy”, which are basically older galaxies that have largely depleted their supplies of dust and gas and therefore do not form new stars.

The team began by taking images of the faint galaxy with the Hubble and then conducting follow-up spectroscopic observations using the ESO/X-Shooter spectrograph – which is part of the Very Large Telescope (VLT) at the Paranal Observatory in Chile. Based on their estimates, the team determined that they were able to amplify the background galaxy by a factor of 30 for the primary image, and a factor of six for the two remaining images.

This makes eMACSJ1341-QG-1 the most strongly amplified quiescent galaxy discovered to date, and by a rather large margin! As Johan Richard – an assistant astronomer at the University of Lyon who performed the lensing calculations, and a co-author on the study – indicated in a University of Hawaii News release:

“The very high magnification of this image provides us with a rare opportunity to investigate the stellar populations of this distant object and, ultimately, to reconstruct its undistorted shape and properties.”

A spiral galaxy ablaze in the blue light of young stars from ongoing star formation (left) and an elliptical galaxy bathed in the red light of old stars (right). Credit: Sloan Digital Sky Survey, CC BY-NC.

Although other extreme magnifications have been conducted before, this discovery has set a new record for the magnification of a rare quiescent background galaxy. These older galaxies are not only very difficult to detect because of their lower luminosity; the study of them can reveal some very interesting things about the formation and evolution of galaxies in our Universe.

As Ebeling, an astronomer with the UH’s Institute of Astronomy and the lead author on the study, explained:

“We specialize in finding extremely massive clusters that act as natural telescopes and have already discovered many exciting cases of gravitational lensing. This discovery stands out, though, as the huge magnification provided by eMACSJ1341 allows us to study in detail a very rare type of galaxy.”

Quiescent galaxies are common in the local Universe, representing the end-point of galactic evolution. As such, this record-breaking find could provide some unique opportunities for studying these older galaxies and determining why star-formation ended in them. As Mikkel Stockmann, a team member from the University of Copenhagen and an expert in galaxy evolution, explained:

“[A]s we look at more distant galaxies, we are also looking back in time, so we are seeing objects that are younger and should not yet have used up their gas supply. Understanding why this galaxy has already stopped forming stars may give us critical clues about the processes that govern how galaxies evolve.”

*An artist’s impression of the accretion disc around the supermassive black hole that powers an active galaxy. Credit: NASA/Dana Berry, SkyWorks Digital*

In a similar vein, recent studies have been conducted that suggest that the presence of a Supermassive Black Hole (SMBH) could be what is responsible for galaxies becoming quiescent. As the powerful jets these black holes create begin to drain the core of galaxies of their dust and gas, potential stars find themselves starved of the material they would need to undergo gravitational collapse.

In the meantime, follow-up observations of eMACSJ1341-QG1 are being conducted using telescopes at the Paranal Observatory in Chile and the Maunakea Observatories in Hawaii. What these observations reveal is sure to tell us much about what will become of our own Milky Way Galaxy someday, when the last of the dust and gas is depleted and all its stars become red giants and long-lived red dwarfs.

Further Reading: University of Hawa’ii News, The Astrophysical Journal Letters

December 15, 2017December 15, 2017 by Matt Williams

Are Little Blue Dots in the Hubble Frontier Fields Precursors to Globular Clusters?

The massive galaxy cluster Abell 370 as seen by Hubble Space Telescope in the final Frontier Fields observations. The lensing effect reveals details about a supernova in the distant universe. Credit: NASA/ESA/HFF

In 2012, the Hubble Space Telescope Frontier Fields program (aka. Hubble Deep Fields Initiative 2012) officially kicked off. The purpose of this project was to study the faintest and most distant galaxies in the Universe using the gravitational lensing technique, thus advancing our knowledge of early galaxy formation. By 2017, the Frontier Field program wrapped up, and the hard work of analyzing all the data it collected began.

One of the more interesting finds within the Frontier Fields data has been the discovery of low mass galaxies with high star formation rates. After examining the “parallel fields” for Abell 2744 and MACS J0416.1-2403 – two galaxy clusters studied by the program – a pair of astronomers noted the presence of what they refer to as “Little Blue Dots” (LBDs), a finding which has implications for galaxy formation and globular clusters.

The study which details their findings recently appeared online under the title “Little Blue Dots in the Hubble Space Telescope Frontier Fields: Precursors to Globular Clusters?“. The study team consisted of Dr. Debra Meloy Elmegreen – a professor of astronomy at Vassar College – and Dr. Bruce G. Elmegreen, an astronomer with the IBM Research Division at the T.J. Watson Research Center in Yorktown Heights.

*The galaxy clusters Abell 2744, MACS J0416.1-2403, MACS J0717.5+3745, MACS J1149.5+2223, Abell S1063, Abell 370. Credit: NASA, ESA, STScI, and the HFF team*

To put it simply, the Frontier Fields program used the Hubble Space Telescope to observe six massive galaxy clusters at optical and near-infrared wavelengths – with its Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3), respectively. These massive galaxies were used to magnify and stretch images of remote galaxies located behind them which were otherwise too faint for Hubble to see directly (aka. gravitational lensing).

While one of these Hubble cameras would look at a galaxy cluster, the other would simultaneously view an adjacent patch of sky. These adjacent patches are known as “parallel fields”, otherwise faint regions that provide some of the deepest looks into the early Universe. As Dr. Bruce Elmegreen told Universe Today via email:

“The purpose of the HFF program is to take deep images of 6 regions of the sky where there are clusters of galaxies, because these clusters magnify background galaxies through the gravitational lens effect. In this way, we can see further than just with direct imaging of the sky alone. Many galaxies have been studied using this magnification technique. The clusters of galaxies are important because they are big mass concentrations which make strong gravitational lenses.”

This six galaxy clusters used for the sake of the project included Abell 2744, MACS J0416.1-2403 and their parallel fields, the latter of which were the focal point in this study. These and the other clusters were used to find galaxies that existed just 600 to 900 million years after the Big Bang. These galaxies and their respective parallels had already been cataloged using computer algorithms that automatically found galaxies in the images and determined their properties.

*Images of the MACS J0416.1–2403 and Abell 2744 galaxy clusters, taken as part of the Hubble Frontier Fields program. Credit: NASA/ESA/HST Frontier Fields team (STScI)*

As the research duo go on to explain in their study, recent large-scale deep surveys have enabled studies of smaller galaxies at higher redshifts. These include “green peas” – luminous, compact and low mass galaxies with high specific star formation rates – and even lower-mass “blueberries”, small starburst galaxies that are a faint extension of the green peas that also show intense rates of star formation.

Using the aforementioned catalogues, and examining the parallel fields for Abell 2744 and MACS J0416.1-2403, the team went looking for other examples of low-mass galaxies with high star formation rates. The purpose of this was to measure the properties of these dwarf galaxies, and to see if any of their positions accorded with where globular clusters are known to have formed.

What they found was what they referred to as “Little Blue Dots” (LBSs), which are even lower-mass versions of “blueberries”. As Dr. Debra Elmegreen told Universe Today via email:

“When I was examining the images (there are about 3400 galaxies detected in each field), I noticed occasional galaxies that appeared as little blue dots, which was very intriguing because of Bruce’s previous theoretical work on dwarf galaxies. The published catalogs included redshifts and star formation rates and masses for each galaxy, and it turns out the little blue dots are low mass galaxies with very high star formation rates for their mass.”

*Close-up view of a HFF parallel field, showing a LBD (upper right). Credit: Debra & Bruce Elmegreen*

These galaxies didn’t show structure, so Debra and Bruce stacked the images of galaxies into 3 different ranges of redshift (which worked out to about 20 galaxies each) to create deeper images. “Still they showed no structure or faint extended outer disk,” said Debra, “so they are at the limit of resolution, with average sizes of 100-200 parsecs (about 300-600 light years) and masses of a few million times the mass of our sun.”

In the end, they determined that within these LBDs, star formation rates were very high. They also noted that these dwarf galaxies were very young, being less than 1% the age of the Universe at the time that they were observed. “So the tiny galaxies just formed,: said Bruce, “and their star formation rates are high enough to account for the globular clusters, maybe one in each LBD, when the star bursts in them wind down after a few tens of million years.”

Debra and Bruce Elmegreen are no strangers to high redshift galaxies. Back in 2012, Bruce published a paper that suggested that the globular clusters that orbit the Milky Way (and most other galaxies) formed in dwarf galaxies during the early Universe. These dwarf galaxies would have since been acquired by larger galaxies like our own, and the clusters are essentially their remnants.

Globular clusters are essentially massive star clusters that orbit around the Milky Way Halo. They are typically around 1 million Solar masses and are made up of stars that are very old – somewhere on the order of 10 to 13 billion years. Beyond the Milky Way, many appear in common orbits and in the Andromeda Galaxy, some even appear connected by a stream of stars.

*The three groups of LBDs, where the dwarf galaxies were stacked based on their redshift. Credit: Debra & Bruce Elmegreen*

As Bruce explained, his is a compelling argument for the theory that globular clusters formed from dwarf galaxies in the early Universe:

“This suggests that the metal-poor globular clusters are the dense remnants of little galaxies that got captured by bigger galaxies, like the Milky Way, and ripped apart by tidal forces. This idea for the origin of halo globular clusters goes back several decades… It would be only the metal-poor one that are like this, which are about half the total, because dwarf galaxies are metal poor compared to big galaxies, and they were also more metal poor in the early universe.”

This study has many implications for our understanding of how the Universe evolved, which was the chief aim of the Hubble Frontier Fields program. By examining objects in the early Universe, and determining their properties, scientists are able to determine how the structures that we are familiar with today – i.e. stars, galaxies, clusters, etc. – truly came from.

These same studies also allow scientists to make educated guesses about where the Universe is going and what will become of those same structures millions or even billions of years from now. In short, knowing where we’ve been lets us predict where we are headed!

Further Reading: arXiv

November 6, 2017November 7, 2017 by Matt Williams

Cutting-Edge Astronomy Confirms Most Ancient Galaxy to Date

Since the deployment of the Hubble Space Telescope, astronomers have been able to look deeper into the cosmic web than ever before. The farther they’ve looked, the deeper back in time they are able to see, and thus learn what the Universe looked like billions of years ago. With the deployment of other cutting-edge telescopes and observatories, scientists have been able to learn a great deal more about the history and evolution of the cosmos.

Most recently, an international team of astronomers using the Gemini North Telescope in Hawaii were able to spot a spiral galaxy located 11 billion light years away. Thanks to a new technique that combined gravitational lensing and spectrography, they were able to see an object that existed just 2.6 billion years after the Big Bang. This makes this spiral galaxy, known as A1689B11, the oldest and most distant spiral galaxy spotted to date.

The study which details the team’s findings, titled “The most ancient spiral galaxy: a 2.6-Gyr-old disk with a tranquil velocity field“, recently appeared in The Astrophysical Journal. The team consisted of members from the Swinburne University of Technology, the Australian Research Council Center of Excellence in All Sky Astrophysics in 3D (ASTRO 3D), the University of Lyon, Princeton University, and the Racah Institute of Physics at The Hebrew University in Jerusalem.

*Spiral galaxy A1689B11 sits behind a massive cluster of galaxies that acts as a lens, producing two magnified images of the spiral galaxy in different positions in the sky. Credit: James Josephides*

Together, the team relied on the gravitational lensing technique to spot A1689B11. This technique has become a mainstay for astronomers, and involves using a large object (like a galaxy cluster) to bend and magnify the light of a galaxy located behind it. As Dr. Tiantian Yuan, a Swinburne astronomer and the lead author on the research study, explained in a Swinburne press statement:

“This technique allows us to study ancient galaxies in high resolution with unprecedented detail. We are able to look 11 billion years back in time and directly witness the formation of the first, primitive spiral arms of a galaxy.”

They then used the Near-infrared Integral Field Spectrograph (NIFS) on the Gemini North telescope to verify the structure and nature of this spiral galaxy. This instrument was built Peter McGregor of The Australian National University (ANU), which now is responsible for maintaining it. Thanks to this latest discovery, astronomers now have some additional clues as to how galaxies took on the forms that we are familiar with today.

Based on the classification scheme developed by famed astronomer Edwin Hubble (the “Hubble Sequence“), galaxies are divides into 3 broad classes based on their shapes – ellipticals, lenticulars and spirals – with a fourth category reserved for “irregularly-shaped” galaxies. In accordance with this scheme, galaxies start out as elliptical structures before branching off to become spiraled, lenticular, or irregular.

*A figure illustrating the Hubble sequence, showing elliptical galaxies (left) and evolving to fit the three broad categories (right) of ellipticals, lenticulars and spirals. Credit: Ville Koistinen*

As such, the discovery of such an ancient spiral galaxy is crucial to determining when and how the earliest galaxies began changing from being elliptical to taking on their modern forms. As Dr Renyue Cen, an astronomer from Princeton University and a co-author on the study, says:

“Studying ancient spirals like A1689B11 is a key to unlocking the mystery of how and when the Hubble sequence emerges. Spiral galaxies are exceptionally rare in the early Universe, and this discovery opens the door to investigating how galaxies transition from highly chaotic, turbulent discs to tranquil, thin discs like those of our own Milky Way galaxy.”

On top of that, this study showed that the A1689B11 spiral galaxy has some surprising features which could also help inform (and challenge) our understanding of this period in cosmic history. As Dr. Yuan explained, these features are in stark contrast to galaxies as they exist today. But equally interesting is the fact that it also differentiates this spiral galaxy from other galaxies that are similar in age.

“This galaxy is forming stars 20 times faster than galaxies today – as fast as other young galaxies of similar masses in the early Universe,” said Dr. Yuan. “However, unlike other galaxies of the same epoch, A1689B11 has a very cool and thin disc, rotating calmly with surprisingly little turbulence. This type of spiral galaxy has never been seen before at this early epoch of the Universe!”

*Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. Credit: NASA and A. Feild (STScI)*

In the future, the team hopes to conduct further studies of this galaxy to further resolve its structure and nature, and to compare it to other spiral galaxies from this epoch. Of particular interest to them is when the onset of spiral arms takes place, which should serve as a sort of boundary marker between ancient elliptical galaxies and modern spiral, lenticular and irregular shapes.

They will continue to rely on the NIFS to conduct these studies, but the team also hopes to rely on data collected by the James Webb Space Telescope (which will be launched in 2019). These and other surveys in the coming years are expected to reveal vital information about the earliest galaxies in the Universe, and reveal further clues as to how it changed over time.

Further Reading: Swinburne, APJ

September 12, 2017 by Matt Williams

Galaxies Swell due to Explosive Action of New Stars

Artist’s impression of a disk galaxy transforming in to an elliptical galaxy. Stars are actively formed in the massive reservoir of dust and gas at the center of the galaxy. Credit: NAOJ

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: ALMA, Astrophysical Journal Letters

May 4, 2017May 4, 2017 by Evan Gough

Enjoy The Biggest Infrared Image Ever Taken Of The Small Magellanic Cloud Without All That Pesky Dust In The Way

The Small Magellanic Cloud is one of the highlights of the southern sky. It can be seen with the naked eye. But it is obscured by clouds of interstellar gas and dust, which makes it hard for optical telescopes to get a good look at it. This image, taken with the ESO's VISTA. is the biggest-ever image of the SMC, and shows millions of stars. Credit: ESO/VISTA VMC

The Small Magellanic Cloud (SMC) galaxy. Credit: ESA/VISTA

The Small Magellanic Cloud (SMC) is one of the Milky Way’s nearest companions (along with the Large Magellanic Cloud.) It’s visible with the naked eye in the southern hemisphere. A new image from the European Southern Observatory’s (ESO) Visible and Infrared Survey Telescope for Astronomy (VISTA) has peered through the clouds that obscure it and given us our biggest image ever of the dwarf galaxy.

The SMC contains several hundred million stars, is about 7,000 light years in diameter, and is about 200,000 light years away. It’s one of the most distant objects that we can see with the naked eye, and can only be seen from the southern hemisphere (and the lowest latitudes of the northern hemisphere.)

The Small Magellanic Cloud is located in the Tucana constellation (The Toucan) in the southern hemisphere. The SMC is shown in green outline around the word 'Tucana'. Also shown are NGC 104 and NGC 362, unrelated objects that are much closer to Earth. Image: ESO, IAU and Sky & Telescope — The Small Magellanic Cloud is located in the Tucana constellation (The Toucan) in the southern hemisphere. The SMC is shown in green outline around the word ‘Tucana’. Also shown are NGC 104 and NGC 362, unrelated objects that are much closer to Earth. Image: ESO, IAU and Sky & Telescope

The SMC is a great target for studying how stars form because it’s so close to Earth, relatively speaking. But the problem is, its detail is obscured by clouds of interstellar gas and dust. So an optical survey of the Cloud is difficult.

But the ESO’s VISTA instrument is ideal for the task. VISTA is a near-infrared telescope, and infrared light is not blocked by the dust. VISTA was built at the ESO’s Paranal Observatory, in the Atacama Desert in Chile where it enjoys fantastic observing conditions. VISTA was designed to perform several surveys, including the Vista Magellanic Survey.

Explore the Zoomable image of the Small Magellanic Cloud. (You won’t be disappointed.)

The VISTA Magellanic Survey is focused on 3 main objectives:

The study of stellar populations in the Magellanic Clouds
The history of star formation in the Magellanic Clouds
The three-dimensional structure of the Magellanic Clouds

An international team led by Stefano Rubele of the University of Padova has studied this image, and their work has produced some surprising results. VISTA has shown us that most of the stars in this image are much younger than stars in other neighbouring galaxies. It’s also shown us that the SMC’s morphology is that of a warped disc. These are only early results, and there’s much more work to be done analyzing the VISTA image.

VISTA inside its enclosure at Paranal. VISTA has a 4.1 meter mirror, and its job is to survey large sections of the sky at once. In the background is the ESO's Very Large Telescope. Image: G. Hüdepohl — VISTA inside its enclosure at Paranal. VISTA has a 4.1 meter mirror, and its job is to survey large sections of the sky at once. In the background is the ESO’s Very Large Telescope. Image: G. Hüdepohl (atacamaphoto.com)/ESO

The team presented their research in a paper titled “The VMC survey – XIV. First results on the look-back time star formation rate tomography of the Small Magellanic Cloud“, published in the journal Monthly Notices of the Royal Astronomical Society.

As the authors say in their paper, the SMC is a great target for study because of its “rich population of star clusters, associations, stellar pulsators, primary distance indicators, and stars in shortlived evolutionary stages.” In a way, we’re fortunate to have the SMC so close. But studying the SMC was difficult, until the VISTA came online with its infrared capabilities.

VISTA saw first light on December 11th, 2009. It’s time is devoted to systematic surveys of the sky. In its first five years, it has undertaken large surveys of the entire southern sky, and also studied small patches of the sky to discern extremely faint objects. The leading image in this article is from the Vista Magellanic Survey, a survey covering 184 square degrees of the sky, taking in both the Small Magellanic Cloud and the Large Magellanic Cloud, and their environment.

Source: VISTA Peeks Through the Small Magellanic Cloud’s Dusty Veil

April 24, 2017April 28, 2017 by Evan Gough

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

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

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:

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.
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.
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.
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.

April 13, 2017April 28, 2017 by Evan Gough

Researchers Image Dark Matter Bridge Between Galaxies

This false color, composite image shows two galaxies, white, connected by a bridge of dark matter, red. The two galaxies are about 40 light years apart. Image: S. Epps & M. Hudson / University of Waterloo

Dark matter is mysterious stuff, because we can’t really “see” it. But that hasn’t stopped scientists from researching it, and from theorizing about it. One theory says that there should be filament structures of dark matter connecting galaxies. Scientists from the University of Waterloo have now imaged one of those dark matter filaments for the first time.

The two scientists, Seth D. Epps and Michael J. Hudson, present their results in a paper at the Monthly Notices of the Royal Astronomy Society.

Theory predicts that filaments of dark matter connect galaxies together, by reaching from the dark matter halo of one galaxy to the same halo in another galaxy. Other researchers have found dark matter filaments connecting entire galaxy clusters, but this is the first time that filaments have been imaged between individual galaxies.

“This image moves us beyond predictions to something we can see and measure.” – Mike Hudson, University of Waterloo

“For decades, researchers have been predicting the existence of dark-matter filaments between galaxies that act like a web-like superstructure connecting galaxies together,” said Mike Hudson, a professor of astronomy at the University of Waterloo. “This image moves us beyond predictions to something we can see and measure.”

Dark matter makes up about 25% of the Universe. But it doesn’t shine, reflect, or interact with light in any way, so it’s difficult to study. The only way we can really study it is by observing gravity. In this study, the pair of astronomers used the weak gravitational lensing technique.

Weak gravitational lensing relies on the effect that mass has on light. Enough concentrated mass in the foreground—dark matter in this case—will warp light from distant sources in the background.

When dealing with something as large as a super-massive Black Hole, gravitational lensing is quite pronounced. But galaxy-to-galaxy filaments of dark matter are much less dense than a black hole, so their individual effect is minimal. What the astronomers needed was the combined data from multiple galaxy pairs in order to detect the weak gravitational lensing.

Key to this study is the Canada-France-Hawaii Telescope. It performed a multi-year sky survey that laid the groundwork for this study. The researchers combined lensing images of over 23,000 pairs of galaxies 4.5 billion light years away. The resulting composite image revealed the filament bridge between the two galaxies.

“By using this technique, we’re not only able to see that these dark matter filaments in the universe exist, we’re able to see the extent to which these filaments connect galaxies together.” – Seth D. Epps, University of Waterloo

We still don’t know what dark matter is, but the fact that scientists were able to predict these filaments, and then actually find them, shows that we’re making progress understanding it.

We’ve known about the large scale structure of the Universe for some time, and we know that dark matter is a big part of it. Galaxies tend to cluster together, under the influence of dark matter’s gravitational pull. Finding a dark matter bridge between galaxies is an intriguing discovery. It at least takes a little of the mystery out of dark matter.

March 29, 2017 by Bob King

Finite Light — Why We Always Look Back In Time

Beads of rainwater on a poplar leaf act like lenses, focusing light and enlarging the leaf’s network of veins. Moving at 186,000 miles per second, light from the leaf arrives at your eye 0.5 nanosecond later. A blink of an eye takes 600,000 times as much time! Credit: Bob King

My attention was focused on beaded water on a poplar leaf. How gemmy and bursting with the morning’s sunlight. I moved closer, removed my glasses and noticed that each drop magnified a little patch of veins that thread and support the leaf.

Focusing the camera lens, I wondered how long it took the drops’ light to reach my eye. Since I was only about six inches away and light travels at 186,000 miles per second or 11.8 inches every billionth of a second (one nanosecond), the travel time amounted to 0.5 nanoseconds. Darn close to simultaneous by human standards but practically forever for positronium hydride, an exotic molecule made of a positron, electron and hydrogen atom. The average lifetime of a PsH molecule is just 0.5 nanoseconds.

Light takes about 35 microseconds to arrive from a transcontinental jet and its contrail. Credit: Bob King

In our everyday life, the light from familiar faces, roadside signs and the waiter whose attention you’re trying to get reaches our eyes in nanoseconds. But if you happen to look up to see the tiny dark shape of a high-flying airplane trailed by the plume of its contrail, the light takes about 35,000 nanoseconds or 35 microseconds to travel the distance. Still not much to piddle about.

The space station orbits the Earth in outer space some 250 miles overhead. During an overhead pass, light from the orbiting science lab fires up your retinas 1.3 milliseconds later. In comparison, a blink of the eye lasts about 300 milliseconds (1/3 of a second) or 230 times longer!

The Lunar Laser Ranging Experiment placed on the Moon by the Apollo 14 astronauts. Observatories beam a laser to the small array, which reflects a bit of the light back. Measuring the time delay yields the Moon’s distance to within about a millimeter. At the Moon’s surface the laser beam spreads out to 4 miles wide and only one photon is reflected back to the telescope every few seconds. Credit: NASA

Light time finally becomes more tangible when we look at the Moon, a wistful 1.3 light seconds away at its average distance of 240,000 miles. To feel how long this is, stare at the Moon at the next opportunity and count out loud: one one thousand one. Retroreflecting devices placed on the lunar surface by the Apollo astronauts are still used by astronomers to determine the moon’s precise distance. They beam a laser at the mirrors and time the round trip.

Venus as a super-thin crescent only 10 hours before conjunction on March 25. The planet was just 2.3 light minutes from the Earth at the time. Credit: Shahrin Ahmad

Of the eight planets, Venus comes closest to Earth, and it does so during inferior conjunction, which coincidentally occurred on March 25. On that date only 26.1 million miles separated the two planets, a distance amounting to 140 seconds or 2.3 minutes — about the time it takes to boil water for tea. Mars, another close-approaching planet, currently stands on nearly the opposite side of the Sun from Earth.

With a current distance of 205 million miles, a radio or TV signal, which are both forms of light, broadcast to the Red Planet would take 18.4 minutes to arrive. Now we can see why engineers pre-program a landing sequence into a Mars’ probe’s computer to safely land it on the planet’s surface. Any command – or change in commands – we might send from Earth would arrive too late. Once a lander settles on the planet and sends back telemetry to communicate its condition, mission control personnel must bite their fingernails for many minutes waiting for light to limp back and bring word.

Before we speed off to more distant planets, let’s consider what would happen if the Sun had a catastrophic malfunction and suddenly ceased to shine. No worries. At least not for 8.3 minutes, the time it takes for light, or the lack of it, to bring the bad news.

Pluto and Charon lie 3.1 billion miles from Earth, a long way for light to travel. We see them as they were more than 4 hours ago. NASA/JHUAPL/SwRI

Light from Jupiter takes 37 minutes to reach Earth; Pluto and Charon are so remote that a signal from the “double planet” requires 4.6 hours to get here. That’s more than a half-day of work on the job, and we’ve only made it to the Kuiper Belt.

Let’s press on to the nearest star(s), the Alpha Centauri system. If 4.6 hours of light time seemed a long time to wait, how about 4.3 years? If you think hard, you might remember what you were up to just before New Year’s Eve in 2012. About that time, the light arriving tonight from Alpha Centauri left that star and began its earthward journey. To look at the star then is to peer back in time to late 2012.

The Summer Triangle rises fully in the eastern sky around 3 o’clock in the morning in late March. Created with Stellarium

But we barely scrape the surface. Let’s take the Summer Triangle, a figure that will soon come to dominate the eastern sky along with the beautiful summer Milky Way that appears to flow through it. Altair, the southernmost apex of the triangle is nearby, just 16.7 light years from Earth; Vega, the brightest a bit further at 25 and Deneb an incredible 3,200 light years away.

We can relate to the first two stars because the light we see on a given evening isn’t that “old.” Most of us can conjure up an image of our lives and the state of world affairs 16 and 25 years ago. But Deneb is exceptional. Photons departed this distant supergiant (3,200 light years) around the year 1200 B.C. during the Trojan War at the dawn of the Iron Age. That’s some look-back time!

Rho Cassiopeia, currently at magnitude +4.5, is one of the most distant stars visible with the naked eye. Its light requires about 8,200 years to reach our eyes. This star, a variable, is enormous with a radius about 450 times that of the Sun. Credit: IAU/Sky and Telescope (left); Anynobody, CC BY-SA 3.0 / Wikipedia

One of the most distant naked eye stars is Rho Cassiopeiae, yellow variable some 450 times the size of the Sun located 8,200 light years away in the constellation Cassiopeia. Right now, the star is near maximum and easy to see at nightfall in the northwestern sky. Its light whisks us back to the end of the last great ice age at a time and the first cave drawings, more than 4,000 years before the first Egyptian pyramid would be built.

This is the digital message (annotated here) sent by Frank Drake to M13 in 1974 using the Arecibo radio telescope.

On and on it goes: the nearest large galaxy, Andromeda, lies 2.5 million light years from us and for many is the faintest, most distant object visible with the naked eye. To think that looking at the galaxy takes us back to the time our distant ancestors first used simple tools. Light may be the fastest thing in the universe, but these travel times hint at the true enormity of space.

Let’s go a little further. On November 16, 1974 a digital message was beamed from the Arecibo radio telescope in Puerto Rico to the rich star cluster M13 in Hercules 25,000 light years away. The message was created by Dr. Frank Drake, then professor of astronomy at Cornell, and contained basic information about humanity, including our numbering system, our location in the solar system and the composition of DNA, the molecule of life. It consisted of 1,679 binary bits representing ones and zeroes and was our first deliberate communication sent to extraterrestrials. Today the missive is 42 light years away, just barely out the door.

Galaxy GN-z11, shown in the inset, is seen as it was 13.4 billion years in the past, just 400 million years after the big bang, when the universe was only three percent of its current age. The galaxy is ablaze with bright, young, blue stars, but looks red in this image because its light has been stretched to longer spectral wavelengths by the expansion of the universe. Credit: NASA, ESA, P. Oesch, G. Brammer, P. van Dokkum, and G. Illingworth

Let’s end our time machine travels with the most distant object we’ve seen in the universe, a galaxy named GN-z11 in Ursa Major. We see it as it was just 400 million years after the Big Bang (13.4 billion years ago) which translates to a proper distance from Earth of 32 billion light years. The light astronomers captured on their digital sensors left the object before there was an Earth, a Solar System or even a Milky Way galaxy!

Thanks to light’s finite speed we can’t help but always see things as they were. You might wonder if there’s any way to see something right now without waiting for the light to get here? There’s just one way, and that’s to be light itself.

From the perspective of a photon or light particle, which travels at the speed of light, distance and time completely fall away. Everything happens instantaneously and travel time to anywhere, everywhere is zero seconds. In essence, the whole universe becomes a point. Crazy and paradoxical as this sounds, the theory of relativity allows it because an object traveling at the speed of light experiences infinite time dilation and infinite space contraction.

Just something to think about the next time you meet another’s eyes in conversation. Or look up at the stars.

February 8, 2017February 15, 2017 by Evan Gough

The Magellenic Clouds Stay Connected By A String Of Stars

This image shows the two "bridges" that connect the Large and Small Magellanic Clouds. The white line traces the bridge of stars that flows between the two dwarf galaxies, and the blue line shows the gas. Image: V. Belokurov, D. Erkal and A. Mellinger

Astronomers have finally observed something that was predicted but never seen: a stream of stars connecting the two Magellanic Clouds. In doing so, they began to unravel the mystery surrounding the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). And that required the extraordinary power of the European Space Agency’s (ESA) Gaia Observatory to do it.

The Large and Small Magellanic Clouds (LMC and SMC) are dwarf galaxies to the Milky Way. The team of astronomers, led by a group at the University of Cambridge, focused on the clouds and on one particular type of very old star: RR Lyrae. RR Lyrae stars are pulsating stars that have been around since the early days of the Clouds. The Clouds have been difficult to study because they sprawl widely, but Gaia’s unique all-sky view has made this easier.

Small and Large Magellanic Clouds over Paranal Observatory Credit: ESO/J. Colosimo

The Mystery: Mass

The Magellanic Clouds are a bit of a mystery. Astronomers want to know if our conventional theory of galaxy formation applies to them. To find out, they need to know when the Clouds first approached the Milky Way, and what their mass was at that time. The Cambridge team has uncovered some clues to help solve this mystery.

The team used Gaia to detect RR Lyrae stars, which allowed them to trace the extent of the LMC, something that has been difficult to do until Gaia came along. They found a low-luminosity halo around the LMC that stretched as far as 20 degrees. For the LMC to hold onto stars that far away means it would have to be much more massive than previously thought. In fact, the LMC might have as much as 10 percent of the mass that the Milky Way has.

The Large Magellanic Cloud. Image: Public Domain, https://commons.wikimedia.org/w/index.php?curid=57110

The Arrival of the Magellanic Clouds

That helped astronomers answer the mass question, but to really understand the LMC and SMC, they needed to know when the clouds arrived at the Milky Way. But tracking the orbit of a satellite galaxy is impossible. They move so slowly that a human lifetime is a tiny blip compared to them. This makes their orbit essentially unobservable.

But astronomers were able to find the next best thing: the often predicted but never observed stellar stream, or bridge of stars, stretching between the two clouds.

A star stream forms when a satellite galaxy feels the gravitational pull of another body. In this case, the gravitational pull of the LMC allowed individual stars to leave the SMC and be pulled toward the LMC. The stars don’t leave at once, they leave individually over time, forming a stream, or bridge, between the two bodies. This action leaves a luminous tracing of their path over time.

The astronomers behind this study think that the bridge actually has two components: stars stripped from the SMC by the LMC, and stars stripped from the LMC by the Milky Way. This bridge of RR Lyrae stars helps them understand the history of the interactions between all three bodies.

A Bridge of Stars… and Gas

The most recent interaction between the Clouds was about 200 million years ago. At that time, the Clouds passed close by each other. This action formed not one, but two bridges: one of stars and one of gas. By measuring the offset between the star bridge and the gas bridge, they hope to narrow down the density of the corona of gas surrounding the Milky Way.

Mystery #2: The Milky Way’s Corona

The density of the Milky Way’s Galactic Corona is the second mystery that astronomers hope to solve using the Gaia Observatory.

The Galactic Corona is made up of ionised gas at very low density. This makes it very difficult to observe. But astronomers have been scrutinizing it intensely because they think the corona might harbor most of the missing baryonic matter. Everybody has heard of Dark Matter, the matter that makes up 95% of the matter in the universe. Dark Matter is something other than the normal matter that makes up familiar things like stars, planets, and us.

The other 5% of matter is baryonic matter, the familiar atoms that we all learn about. But we can only account for half of the 5% of baryonic matter that we think has to exist. The rest is called the missing baryonic matter, and astronomers think it’s probably in the galactic corona, but they’ve been unable to measure it.

A part of the Small Magellanic Cloud galaxy is dazzling in this image from NASA’s Great Observatories. The Small Magellanic Cloud is about 200,000 light-years way from our own Milky Way spiral galaxy. Credit: NASA.

Understanding the density of the Galactic Corona feeds back into understanding the Magellanic Clouds and their history. That’s because the bridges of stars and gas that formed between the Small and Large Magellanic Clouds initially moved at the same speed. But as they approached the Milky Way’s corona, the corona exerted drag on the stars and the gas. Because the stars are small and dense relative to the gas, they travelled through the corona with no change in their velocity.

But the gas behaved differently. The gas was largely neutral hydrogen, and very diffuse, and its encounter with the Milky Way’s corona slowed it down considerably. This created the offset between the two streams.

Eureka?

The team compared the current locations of the streams of gas and stars. By taking into account the density of the gas, and also how long both Clouds have been in the corona, they could then estimate the density of the corona itself.

When they did so, their results showed that the missing baryonic matter could be accounted for in the corona. Or at least a significant fraction of it could. So what’s the end result of all this work?

It looks like all this work confirms that both the Large and Small Magellanic Clouds conform to our conventional theory of galaxy formation.

Mystery solved. Way to go, science.

January 3, 2017January 3, 2017 by Matt Williams

What is the Closest Galaxy to the Milky Way?

Image showing nearly 50,000 galaxies in the nearby universe detected by the Two Micron All Sky Survey (2MASS) in infrared light. Credit: 2MASS/ T. H. Jarrett/J. Carpenter/R. Hurt

Scientists have known for some time that the Milky Way Galaxy is not alone in the Universe. In addition to our galaxy being part of the Local Group – a collection of 54 galaxies and dwarf galaxies – we are also part of the larger formation known as the Virgo Supercluster. So you could say the Milky Way has a lot of neighbors.

Of these, most people consider the Andromeda Galaxy to be our closest galactic cohabitant. But in truth, Andromeda is the closest spiral galaxy, and not the closest galaxy by a long shot. This distinction falls to a formation that is actually within the Milky Way itself, a dwarf galaxy that we’ve only known about for a little over a decade.

Closest Galaxy:

At present, the closet known galaxy to the Milky Way is the Canis Major Dwarf Galaxy – aka. the Canis Major Overdensity. This stellar formation is about 42,000 light years from the galactic center, and a mere 25,000 light years from our Solar System. This puts it closer to us than the center of our own galaxy, which is 30,000 light years away from the Solar System.

Illustration of the Canis Dwarf Dwarf Galaxy, Credit: R. Ibata (Strasbourg Observatory, ULP) et al./2MASS/NASA — *Illustration of the Canis Dwarf Galaxy and its associated tidal (shown in red) in relation to our Milky Way. Credit: R. Ibata (Strasbourg Observatory, ULP) et al./2MASS/NASA*

Characteristics:

The Canis Major Dwarf Galaxy Dwarf Galaxy is believed to contain one billion stars in all, a relatively high-percentage of which are in the Red Giant Branch phase of their lifetimes. It has a roughly elliptical shape and is thought to contain as many stars as the Sagittarius Dwarf Elliptical Galaxy, the previous contender for closest galaxy to our location in the Milky Way.

In addition to the dwarf galaxy itself, a long filament of stars is visible trailing behind it. This complex, ringlike structure – which is sometimes referred to as the Monoceros Ring – wraps around the galaxy three times. The stream was first discovered in the early 21st century by astronomers conducting the Sloan Digital Sky Survey (SDSS).

It was in the course of investigating this ring of stars, and a closely spaced group of globular clusters similar to those associated with the Sagittarius Dwarf Elliptical Galaxy, that the Canis Major Dwarf Galaxy was first discovered. The current theory is that this galaxy was accreted (or swallowed up) by the Milky Way Galaxy.

Other globular clusters that orbit the center of our Milky Way as a satellite – i.e. NGC 1851, NGC 1904, NGC 2298 and NGC 2808 – are thought to have been part of the Canis Major Dwarf Galaxy before its accretion. It also has associated open clusters, which are thought to have formed as a result of the dwarf galaxy’s gravity perturbing material in the galactic disk and stimulating star formation.

*Images of a few examples of merging galaxies taken by the Hubble Space Telescope. Credit: NASA/ESA/STScI/A. Evans/NRAO/Caltech*

Discovery:

Prior to its discovery, astronomers believed that the Sagittarius Dwarf Galaxy was the closest galactic formation to our own. At 70,000 light years from Earth, this galaxy was determined in 1994 to be closer to us than the Large Magellanic Cloud (LMC), the irregular dwarf galaxy that is located 180,000 light years from Earth, and which previously held the title of the closest galaxy to the Milky Way.

All of that changed in 2003 when The Canis Major Dwarf Galaxy was discovered by the Two Micron All-Sky Survey (2MASS). This collaborative astronomical mission, which took place between 1997 and 2001, relied on data obtained by the Mt. Hopkins Observatory in Arizona (for the Northern Hemisphere) and the Cerro Tololo Inter-American Observatory in Chile (for the southern hemisphere).

From this data, astronomers were able to conduct a survey of 70% of the sky, detecting about 5,700 celestial sources of infrared radiation. Infrared astronomy takes advantage of advances in astronomy that see more of the Universe, since infrared light is not blocked by gas and dust to the same extent as visible light.

Because of this technique, the astronomers were able to detect a very significant over-density of class M giant stars in a part of the sky occupied by the Canis Major constellation, along with several other related structures composed of this type of star, two of which form broad, faint arcs (as seen in the image close to the top).

*An artist depicts the incredibly powerful flare that erupted from the red dwarf star EV Lacertae. Credit: Casey Reed/NASA*

The prevalence of M-class stars is what made the formation easy to detect. These cool, “Red Dwarfs” are not very luminous compared to other classes of stars, and cannot even be seen with the naked eye. However, they shine very brightly in the infrared, and appeared in great numbers.

The discovery of this galaxy, and subsequent analysis of the stars associated with it, has provided some support for the current theory that galaxies may grow in size by swallowing their smaller neighbors. The Milky Way became the size it is now by eating up other galaxies like Canis Major, and it continues to do so today. And since stars from the Canis Major Dwarf Galaxy are technically already part of the Milky Way, it is by definition the nearest galaxy to us.

As already noted, it was the Sagittarius Dwarf Elliptical Galaxy that held the position of closest galaxy to our own prior to 2003. At 75,000 light years away. This dwarf galaxy, which consists of four globular clusters that measure some 10,000 light-years in diameter, was discovered in 1994. Prior to that, the Large Magellanic Cloud was thought to be our closest neighbor.

The Andromeda Galaxy (M31) is the closest spiral galaxy to us, and though it’s gravitationally bound to the Milky Way, it’s not the closest galaxy by far – being 2 million light years away. Andromeda is currently approaching our galaxy at a speed of about 110 kilometers per second. In roughly 4 billion years, the Andromeda Galaxy is expected to merge with out own, forming a single, super-galaxy.

Future of the Canis Major Dwarf Galaxy:

Astronomers also believe that the Canis Major Dwarf Galaxy is in the process of being pulled apart by the gravitational field of the more massive Milky Way Galaxy. The main body of the galaxy is already extremely degraded, a process which will continue as it travels around and through our Galaxy.

In time, the accretion process will likely culminate with the Canis Major Dwarf Galaxy merging entirely with the Milky Way, thus depositing its 1 billion stars to the 200 t0 400 billion that are already part of our galaxy.

We have written many interesting articles on galaxies here at Universe Today. Here’s Closest Galaxy Discovered, How did the Milky Way Form?, How Many Galaxies are there in the Universe?, What is the Milky Way Collision, Spiral Galaxies Could eat Dwarfs all over the Universe and The Canis Major Constellation.

For more information, check out this article from the Spitzer Space Telescope‘s website about the galaxies that are closest to the Milky Way Galaxy. And here is a video by the same author on the subject.

Astronomy Cast has some interesting episodes on the subject. Here’s Episode 97: Galaxies and Episode 99: The Milky Way.

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