The Magellanic Clouds are two of our closest neighbours, in galactic terms. The pair of irregular dwarf galaxies were drawn into the Milky Way’s orbit in the distant past, and we’ve been looking up at them since the dawn of humanity. Some of our ancestors even gathered pigments and created images of them in petroglyphs and cave paintings.
Following in the footsteps of those ancient artists, astronomers recently used the Dark Energy Camera (DECam) to capture an in-depth portrait of the pair of galaxies.
The Magellanic Clouds are a pair of dwarf galaxies that are bound to the Milky Way. The Milky Way is slowly consuming them in Borg-like fashion, starting with the gas halo that surrounds both Clouds. They’re visible in the southern sky, and for centuries people have gazed up at them. They’re named after the Portuguese explorer Ferdinand Magellan, in our current times.
Massive galaxies like our Milky Way gain mass by absorbing smaller galaxies. The Large Magellanic Cloud and the Small Magellanic Cloud are irregular dwarf galaxies that are gravitationally bound to the Milky Way. Both the clouds are distorted by the Milky Way’s gravity, and astronomers think that the Milky Way is in the process of digesting both galaxies.
A new study says that process is already happening, and that the Milky Way is enjoying the Magellanic Clouds’ halos of gas as an appetizer, creating a feature called the Magellanic Stream as it eats. It also explains a 50 year old mystery: Why is the Magellanic Stream so massive?
For some time, astronomers have known that collisions or mergers between galaxies are an integral part of cosmic evolution. In addition to causing galaxies to grow, these mergers also trigger new rounds of star formation as fresh gas and dust are injected into the galaxy. In the future, astronomers estimate that the Milky Way Galaxy will merge with the Andromeda Galaxy, as well as the Small and Large Magellanic Clouds in the meantime.
According to new results obtained by researchers at the Flatiron Institute’s Center for Computational Astrophysics (CCA) in New York city, the results of our eventual merger with the Magellanic Clouds is already being felt. According to results presented at the 235th meeting of the American Astronomical Society this week, stars forming in the outskirts of our galaxy could be the result of these dwarf galaxies merging with our own.
On December 19th, 2013, the European Space Agency’s (ESA) Gaia spacecraft took to space with for a very ambitious mission. Over the course of its planned 5-year mission (which was recently extended), this space observatory would map over a billion stars, planets, comets, asteroids and quasars in order to create the largest and most precise 3D catalog of the Milky Way ever created.
Since that time, the ESA has made two data releases that cover the first three years of the Gaia mission. The second data release, which took on April 25th, 2018, has already proven to be a treasure trove for astronomers. In addition to the positions, distance indicators and motions of over a billion stars and celestial objects in the Milky Way Galaxy, it also contained a hidden gem – the proper motions of stars within the Large Magellanic Cloud (LMC).
Located about 200,000 light-years from Earth, the LMC has dense clouds of dust that results in it experiencing high rates of star formation. In addition, it’s central bar is warped (where the east and west ends are nearer to the Milky Way), suggesting that it was once a barred dwarf spiral galaxy who’s spiral arms were disrupted by interaction with the Small Magellanic Cloud (SMC) and the Milky Way.
For these reasons, astronomers have been hoping to derive the orbits of dwarf galaxies (and globular clusters) that revolve around the Milky Way. In so doing, they hope to learn more about how our galaxy evolved due to mergers with clusters and other galaxies. By determining the proper motions of the LMC’s stars, the Gaia mission has provided clues as to how the Milky Way and its largest satellite galaxy have interacted over time.
As you can see from the image (at top), the bar of the LMC is outlined in great detail, along with individual star-forming regions like the Tarantula Nebula (aka. 30 Doradus, which is visible just above the center of the galaxy). The image combines the total amount of radiation detected by the observatory in each pixel. The radiation measurements were then taken through different filters on the spacecraft to generate color information.
This allowed Gaia to obtain information about the total density of stars within the LMC as well as their proper motions. As you can see, the image is dominated by the brightest, most massive stars, which greatly outshine their fainter, lower-mass counterparts. The proper motions of the stars observed is represented as the texture of the image – which looks a lot like a fingerprint.
From this, scientists were able to see an imprint of the stars rotating clockwise around the center of the galaxy. Using this information, astronomers will be able to create new models on how the LMC, SMC, and Milky Way evolved together over time. This, in turn, could shed light on how galaxies like our own, formed and evolved over the course of billions of years.
As with other information contained in the first and second data releases, this latest discovery demonstrates that the Gaia mission is fulfilling its intended purpose. The third release of Gaia data is scheduled to take place in late 2020, with the final catalog being published in the 2020s. Meanwhile, an extension has already been approved for the Gaia mission, which will now remain in operation until the end of 2020 (to be confirmed at the end of this year).
And be sure to enjoy this animated view of the LMC’s rotation, courtesy of the ESA:
The Hubble Space Telescope has revealed some amazing things over the past few decades. Over the course of its many missions, this orbiting observatory has spotted things ranging from distant stars and galaxies to an expanding Universe. And today, twenty-six years later, it is still providing us with rare glimpses of the cosmos.
For example, just in time for the holidays, Hubble has released images of two rosy, glowing nebulas in the Small Magellanic Cloud (SMC). These glowing clouds of gas and dust were spotted as part of a study known as the Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE), an effort to study this neighboring galaxy in an attempt to better understand our own.
The images were taken by Hubble’s Advanced Camera for Surveys (ACS) in September 2015 and feature NGC 248 – two gaseous nebulas that were first observed by astronomer Sir John Herschel in 1834 and are situated in such a way as to appear as one. Measuring about 60 light years in length and 20 light-years in width, these nebulas are among a series of emission nebulas located in the neighboring dwarf satellite galaxy.
Emission nebulas are essentially large clouds of ionized gases that emit light of various colors – in this case, bright red. The color and luminosity of NGC 248 is due to the nebulas heavy hydrogen content, and the fact that they have young, brilliant stars at the center of them. These stars emit intense radiation that heats up the hydrogen gas, causing it to emit bright red light.
As noted, the images were taken as part of the SMIDGE study, an effort on behalf of astronomers to probe the Milky Way satellite – which is located approximately 200,000 light-years away in the southern constellation Tucana – using the Hubble Space Telescope. The ultimate goal of this study is to understand how dust is different in galaxies that have a far lower supply of the heavy elements needed to create it.
In the case of the SMC, it has between one-fifth and one-tenth the amount of heavy metals as the Milky Way. In addition, its proximity to the Milky Way makes it a convenient target for astronomers who are looking to better understand the history of the earlier Universe. Essentially, most star formation in the Milky Way happened at a time when the amount of heavy elements was much lower than it is now.
According to Dr. Karin Sandstrom, a professor from the University of California and the principle investigator of SMIDGE, studying the SMC’s can tell us much about neighboring galaxies, but also about the evolution of the Milky Way. “It is important for understanding the history of our own galaxy, too,” he said. “Dust is a really critical part of how a galaxy works, how it forms stars.”
In addition to the stunning images, the SMIDGE team and the Space Telescope Science Institute have also produced a video that shows the location of NGC 248 in the southern sky. As you can see, the video begins with a ground-based view of the night sky (from the southern hemisphere) and then zooms in on the Small Magellanic Cloud, emphasizing the field where NGC 249 appears.
Check out the video below, and have yourselves a Merry Christmas and some Happy Holidays!
Since ancient times, human beings have been staring at the night sky and been amazed by the celestial objects looking back at them. Whereas these objects were once thought to be divine in nature, and later mistaken for comets or other astrological phenomena, ongoing observation and improvements in instrumentation have led to these objects being identified for what they are.
For example, there are the Small and Large Magellanic Clouds, two large clouds of stars and gas that can be seen with the naked eye in the southern hemisphere. Located at a distance of 200,000 and 160,000 light years from the Milky Way Galaxy (respectively), the true nature of these objects has only been understand for about a century. And yet, these objects still have some mysteries that have yet to be solved.
The Large Magellanic Cloud (LMC) and the neighboring the Small Magellanic Cloud (SMC) are starry regions that orbit our galaxy, and look conspicuously like detached pieces of the Milky Way. Though they are separated by 21 degrees in the night sky – about 42 times the width of the full moon – their true distance is about 75,000 light-years from each other.
The Large Magellanic Cloud is located about 160,000 light-years from the Milky Way, in the constellation Dorado. This makes it the 3rd closest galaxy to us, behind the Sagittarius Dwarf and Canis Major Dwarf galaxies. Meanwhile, the Small Magellanic Cloud is located in the constellation of Tucana, about 200,000 light-years away.
The LMC is roughly twice the diameter of the SMC, measuring some 14,000 light-years across vs. 7,000 light years (compared to 100,000 light years for the Milky Way). This makes it the 4th largest galaxy in our Local Group of galaxies, after the Milky Way, Andromeda and the Triangulum Galaxy. The LMC is about 10 billion times as massive as our Sun (about a tenth the mass of the Milky Way), while the SMC is equivalent to about 7 billion Solar Masses.
In terms of structure, astronomers have classified the LMC as an irregular type galaxy, but it does have a very prominent bar in its center. Ergo, it’s possible that it was a barred spiral before its gravitational interactions with the Milky Way. The SMC also contains a central bar structure and it is speculated that it too was once a barred spiral galaxy that was disrupted by the Milky Way to become somewhat irregular.
Aside from their different structure and lower mass, they differ from our galaxy in two major ways. First, they are gas-rich – meaning that a higher fraction of their mass is hydrogen and helium – and they have poor metallicity, (meaning their stars are less metal-rich than the Milky Way’s). Both possess nebulae and young stellar populations, but are made up of stars that range from very young to the very old.
In fact, this abundance in gas is what ensures that the Magellanic Clouds are able to create new stars, with some being only a few hundred million years in age. This is especially true of the LMC, which produces new stars in large quantities. A good example of this is it’s glowing-red Tarantula Nebula, a gigantic star-forming region that lies 160,000 light-years from Earth.
Astronomers estimate that the Magellanic Clouds were formed approximately 13 billion years ago, around the same time as the Milky Way Galaxy. It has also been believed for some time that the Magellanic Clouds have been orbiting the Milky Way at close to their current distances. However, observational and theoretical evidence suggests that the clouds have been greatly distorted by tidal interactions with the Milky Way as they travel close to it.
This indicates that they are not likely to have frequently got as close to the Milky Way as they are now. For instance, measurements conducted with the Hubble Space Telescope in 2006 suggested that the Magellanic Clouds may be moving too fast to be long terms companions of the Milky Way. In fact, their eccentric orbits around the Milky Way would seem to indicate that they came close to our galaxy only once since the universe began.
This was followed in 2010 by a study that indicated that the Magellanic Clouds may be passing clouds that were likely expelled from the Andromeda Galaxy in the past. The interactions between the Magellanic Clouds and the Milky Way is evidenced by their structure and the streams of neutral hydrogen that connects them. Their gravity has affected the Milky Way as well, distorting the outer parts of the galactic disk.
History of Observation:
In the southern hemisphere, the Magellanic clouds were a part of the lore and mythology of the native inhabitants, including the Australian Aborigines, the Maori of New Zealand, and the Polynesian people of the South Pacific. For the latter, they served as important navigational markers, while the Maori used them as predictors of the winds.
While the study Magellanic Clouds dates back to the 1st millennium BCE, the earliest surviving record comes from the 10th century Persian astronomer Al Sufi. In his 964 treatise, Book of Fixed Stars, he called the LMC al-Bakr (“the Sheep”) “of the southern Arabs”. He also noted that the Cloud is not visible from northern Arabia or Baghdad, but could be seen at the southernmost tip of Arabian Peninsula.
By the late 15th century, Europeans are believed to have become acquainted with the Magellanic Clouds thanks to exploration and trade missions that took them south of the equator. For instance, Portuguese and Dutch sailors came to know them as the Cape Clouds, since they could only be viewed when sailing around Cape Horn (South America) and the Cape of Good Hope (South Africa).
During the circumnavigation of the Earth by Ferdinand Magellan (1519–22), the Magellanic Clouds were described by Venetian Antonio Pigafetta (Magellan’s chronicler) as dim clusters of stars. In 1603, German celestial cartographer Johann Bayer published his celestial atlas Uranometria, where he named the smaller cloud “Nebecula Minor” (Latin for “Little Cloud”).
Between 1834 and 1838, English astronomer John Herschel conducted surveys of the southern skies from the Royal Observatory at the Cape of Good Hope. While observing the SMC, he described it as a cloudy mass of light with an oval shape and a bright center, and catalogued a concentration of 37 nebulae and clusters within it.
In 1891, the Harvard College Observatory opened an observing station in southern Peru. From 1893-1906, astronomers used the observatory’s 61 cm (24 inch) telescope to survey and photograph the LMC and SMC. One such astronomers was Henriette Swan Leavitt, who used the observatory to discover Cephied Variable stars in the SMC.
Her findings were published in 1908 a study titled “1777 variables in the Magellanic Clouds“, in which she showed the relationship between these star’s variability period and luminosity – which became a very reliable means of determining distance. This allowed the SMCs distance to be determined, and became the standard method of measuring the distance to other galaxies in the coming decades.
As noted already, in 2006, measurements made suing the Hubble Space Telescope were announced that suggested the Large and Small Magellanic Clouds may be moving too fast to be orbiting the Milky Way. This has given rise to the theory that they originated in another galaxy, most likely Andromeda, and were kicked out during a galactic merger.
Given their composition, these clouds – especially the LMC – will continue making new stars for some time to come. And eventually, millions of years from now, these clouds may merge with our own Milky Way Galaxy. Or, they could keep orbiting us, passing close enough to suck up hydrogen and keep their star-forming process going.
But in a few billion years, when the Andromeda Galaxy collides with our own, they may find themselves having no choice but to merge with the giant galaxy that results. One might say Andromeda regrets spitting them out, and is coming to collect them!
Now that’s pure gorgeous. As Comet C/2013 A1 Siding Spring sidles towards its October 19th encounter with Mars, it’s passing a trio of sumptuous deep sky objects near the south celestial pole this week. Astrophotographers weren’t going to let the comet’s picturesque alignments pass without notice. Rolando Ligustri captured this remarkable view using a remote, computer-controlled telescope on August 29th. It shows the rich assemblage of stars and star clusters that comprise the Small Magellanic Cloud, one of the Milky Way’s satellite galaxies located 200,000 light years away.
Looking like a fuzzy caterpillar, Siding Spring seems to crawl between the little globular cluster NGC 362 and the rich swarm called 47 Tucanae, one of the few globulars bright enough to see with the naked eye. C/2013 A1 is currently circumpolar from many locations south of the equator and visible all night long. Glowing at around magnitude +9.5 with a small coma and brighter nucleus, a 6-inch or larger telescope will coax it from a dark sky. Siding Spring dips farthest south on September 2-3 (Dec. -74º) and then zooms northward for Scorpius and Sagittarius. It will encounter additional deep sky objects along the way, most notably the bright open cluster M7 on October 5-6, before passing some 82,000 miles from Mars on October 19th.
While the chance of a Mars impact is near zero, the fluffy comet’s fluffy coma and broad tail, both replete with tiny but fast-moving (~125,000 mph) dust particles, might pose a hazard for spacecraft orbiting the Red Planet. Assuming either coma or tail grows broad enough to sweep across the Martian atmosphere, impacting dust might create a spectacular meteor shower. Mars Rover cameras may be used to photograph the comet before the flyby and to capture meteors during its closest approach. NASA plans to ‘hide’ its orbiting probes on the opposite side of the planet for a brief time during the approximately 4-hour-long encounter just in case.
Today, Siding Spring’s coma or temporary atmosphere measures about 12,000 miles (19,300 km) wide. While I can’t get my hands on current dust production rates, in late January, when it was farther from the sun than at present, C/2013 A1 kicked out ~800,000 lbs per hour (~100 kg/sec). On October 19th, observers across much of the globe with 6-inch or larger instruments will witness the historic encounter with their own eyes at dusk in the constellation Sagittarius.
One has never been spotted for sure in the wild jungle of strange stellar objects out there, but astronomers now think they have finally found a theoretical cosmic curiosity: a Thorne-Zytkow Object, or TZO, hiding in the neighboring Small Magellanic Cloud. With the outward appearance of garden-variety red supergiants, TZOs are actually two stars in one: a binary pair where a super-dense neutron star has been absorbed into its less dense supergiant parter, and from within it operates its exotic elemental forge.
First theorized in 1975 by physicist Kip Thorne and astronomer Anna Zytkow, TZOs have proven notoriously difficult to find in real life because of their similarity to red supergiants, like the well-known Betelgeuse at the shoulder of Orion. It’s only through detailed spectroscopy that the particular chemical signatures of a TZO can be identified.
Observations of the red supergiant HV 2112 in the Small Magellanic Cloud*, a dwarf galaxy located a mere 200,000 light-years away, have revealed these signatures — unusually high concentrations of heavy elements like molybdenum, rubidium, and lithium.
While it’s true that these elements are created inside stars — we are all star-stuff, like Carl Sagan said — they aren’t found in quantity within the atmospheres of lone supergiants. Only by absorbing a much hotter star — such as a neutron star left over from the explosive death of a more massive partner — is the production of such elements presumed to be possible.
“Studying these objects is exciting because it represents a completely new model of how stellar interiors can work,”said Emily Levesque, team leader from the University of Colorado Boulder and lead author on the paper. “In these interiors we also have a new way of producing heavy elements in our universe.”
Definitive detection of a TZO would provide direct evidence for a completely new model of stellar interiors, as well as confirm a theoretically predicted fate for massive star binary systems and the existence of nucleosynthesis environments that offer a new channel for heavy-element and lithium production in our universe.
– E.M. Levesque et al., Discovery of a Thorne-Zytkow object candidate in the Small Magellanic Cloud
One of the original proposers of TZOs, Dr. Anna Zytkow, is glad to see her work resulting in new discoveries.
“I am extremely happy that observational confirmation of our theoretical prediction has started to emerge,” Zytkow said. “Since Kip Thorne and I proposed our models of stars with neutron cores, people were not able to disprove our work. If theory is sound, experimental confirmation shows up sooner or later. So it was a matter of identification of a promising group of stars, getting telescope time and proceeding with the project.”
The findings were first announced in January at the 223rd meeting of the American Astronomical Society. The paper has now been accepted for publication in the Monthly Notices of the Royal Astronomical Society Letters, and is co-authored by Philip Massey, of Lowell Observatory in Flagstaff, Arizona; Anna Zytkow of the University of Cambridge in the U.K.; and Nidia Morrell of the Carnegie Observatories in La Serena, Chile. Read the team’s paper here.
Source: University of Colorado, Boulder. Illustration by ‘Digital Drew.’
__________________________ *In the paper the team notes that it’s not yet confirmed that HV 2112 is part of the SMC and could be associated with our own galaxy. If so it would rule out it being a TZO, but would still require an explanation of its observed spectra.
As the Milky Way rises over the horizon at the European Southern Observatory, its companion galaxies also come into view. Credit: ESO/Y. Beletsky
A previously undetected heist of stars was uncovered by astronomers who were actually looking for why an unexpected amount of microlensing events were being seen around the outskirts of the Milky Way. Instead, they found the Large Magellanic Cloud (LMC) had been stealing stars from its neighbor, the Small Magellanic Cloud (SMC), leaving behind a trail of stars. Although the crime was likely committed hundreds of milllions of years ago during a collision between the two galaxies, the new information is helping astronomers to understand the history of these two galaxies that are in our neighborhood.
“You could say we discovered a crime of galactic proportions,” said Avi Loeb of the Harvard-Smithsonian Center for Astrophysics.
The Large Magellanic Cloud almost got away with it, if it wasn’t for those meddling astronomers….
Astronomers were originally monitoring the LMC to hunt for the reason for the unexpected microlensing events. Their initial hypothesis was that massive compact halo objects, or MACHOs were causing the effect, where a nearby object passes in front of a more distant star. The gravity of the closer object bends light from the star like a lens, magnifying it and causing it to brighten. The MACHOs were thought to be faint objects, roughly the mass of a star, but not much is known about them. Several surveys looked for MACHOs in order to find out if they could be a major component of dark matter – the unseen stuff that holds galaxies together.
In order for MACHOs to make up dark matter, they must be so faint that they can’t be directly detected. So, the team of astronomers hoped to see MACHOs within the Milky Way by lensing distant LMC stars.
“We originally set out to understand the evolution of the interacting LMC and SMC galaxies,” said lead author of a new paper on the results, Gurtina Besla of Columbia University. “We were surprised that, in addition, we could rule out the idea that dark matter is contained in MACHOs.”
“Instead of MACHOs, a trail of stars removed from the SMC is responsible for the microlensing events,” said Loeb.
Only a fast-moving population of stars could yield the observed rate and durations of the microlensing events. The best way to get such a stellar population is a galactic collision, which appears to have occurred in the LMC-SMC system.
“By reconstructing the scene, we found that the LMC and SMC collided violently hundreds of millions of years ago. That’s when the LMC stripped out the lensed stars,” said Loeb.
Their research also supports recent findings suggesting that both Magellanic Clouds are on their first pass by the Milky Way.
However, this isn’t a closed case. The evidence for the trail of lensed stars is persuasive, but they haven’t been directly observed yet. A number of teams are searching for the signatures of these stars within a bridge of gas that connects the Magellanic Clouds.
The simulation results will be published in the Monthly Notices of the Royal Astronomical Society.