A false colour composite of the distribution of water and hydroxyl molecules over the lunar surface. Credit: ISRO/NASA/JPL-Caltech/Brown Univ./USGS
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The recent discovery of water on the Moon may have a serious impact on future plans for lunar based astronomy. Space scientists from the Chinese Academy of Sciences have calculated that the scattering caused by molecules vaporized in sunlight could heavily distort observations from telescopes mounted on the Moon.
“Last year, scientists discovered a fine dew of water covering the Moon. This water vaporizes in sunlight and is then broken down by ultraviolet radiation, forming hydrogen and hydroxyl molecules. We recalculated the amount of hydroxyl molecules that would be present in the lunar atmosphere and found that it could be two or three orders higher than previously thought,” said Zhao Hua, who presented his team’s results at the European Planetary Science Congress in Rome.
The research has particular implications for the Chinese Lunar lander, Chang’E-3, which is planned to be launched in 2013. An ultraviolet astronomical telescope will be installed on the Chang’E-3 lander, which will operate on the sunlit surface of the Moon, powered by solar panels.
“At certain ultraviolet wavelengths, hydroxyl molecules cause a particular kind of scattering where photons are absorbed and rapidly re-emitted. Our calculations suggest that this scattering will contaminate observations by sunlit telescopes,” said Zhao.
The Moon’s potential as a site for building astronomical observatories has been discussed since the era of the Space Race. Lunar-based telescopes could have several advantages over astronomical telescopes on Earth, including a cloudless sky and low seisimic activity.
The far-side of the Moon could be an ideal site for radio astronomy, being permanently shielded from interference from the Earth. Radio observations would not be affected by the higher hydroxyl levels.
The Small and Large Magellanic Clouds - not the kind of things you usually find near large spiral galaxies. Cerro Tololo observatory, Credit: Fred Walker.
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Sorry – a bit of southern sky bias in this one. But it does seem that our favourite down under naked eye objects are even more unique than we might have thought. The two dwarf galaxies, the Large and Small Magellanic Clouds, orbit the Milky Way and have bright star forming regions. It would seem that most satellite galaxies, in orbit around other big galaxies, don’t. And, taking this finding a step further, our galaxy may be one of a declining minority of galaxies still dining on gas-filled dwarf galaxies to maintain a bright and youthful appearance.
We used to think that the Sun was an ordinary, unremarkable star – but these days we should acknowledge that it’s out of statistical mid-range, since the most common stars in the visible universe are red dwarfs. Also, most stars are in binary or larger groups – unlike our apparently solitary one.
The Sun is also fortunately positioned in the Milky Way’s habitable zone – not too close-in to be constantly blasted with gamma rays, but close-in enough for there to be plenty of new star formation to seed the interstellar medium with heavy elements. And the Milky Way itself is starting to look a bit out of the ordinary. It’s quite large as spiral galaxies go, bright with active star formation – and it’s got bright satellites.
The Lambda Cold Dark Matter (CDM) model of large scale structure and galaxy formation has it that galaxy formation is a bottom-up process, with the big galaxies we see today having formed from the accretion of smaller structures – including dwarf galaxies – which themselves may have first formed upon some kind of dark matter scaffolding.
Through this building-up process, spinning spiral galaxies with bright star forming regions should become common place – only dimming if they run out of new gas and dust to feast on, only losing their structure if they collide with another big galaxy – first becoming a ‘train wreck’ irregular galaxy and then probably evolving into an elliptical galaxy.
The Lambda CDM model suggests that other bright spiral galaxies should also be surrounded by lots of gas-filled satellite galaxies, being slowly draw in to feed their host. Otherwise how is it that these spiral galaxies get so big and bright? But, at least for the moment, that’s not what we are finding – and the Milky Way doesn’t seem to be a ‘typical’ example of what’s out there.
The relative lack of satellites observed around other galaxies could mean the era of rapidly accreting and growing galaxies is coming to a close – a point emphasised by the knowledge that we observe distant galaxies at various stages of their past lives anyway. So the Milky Way may already be a relic of a bygone era – one of the last of the galaxies still growing from the accretion of smaller dwarf galaxies.
Supernova 1987a, which exploded near the Tarantula Nebula of the Large Magellanic Cloud. Credit: Anglo-Australian Observatory.
On the other hand – maybe we just have some very unusual satellites. To a distant observer, the Large MC would have nearly a tenth of the luminosity of the Milky Way and the Small MC nearly a fortieth– we don’t find anything like this around most other galaxies. The Clouds may even represent a binary pair which is also fairly unprecedented in any current sky survey data.
They are thought to have passed close together around 2.5 billion years ago – and it’s possible that this event may have set off an extended period of new star formation. So maybe other galaxies do have lots of satellites – it’s just that they are dim and difficult to observe as they are not engaged in new star formation.
Either way, using our galaxy as a basis for modelling how other galaxies work might not be a good idea – apparently it’s not so ordinary.
The Hubble sequence is astronomer’s main tool for classifying galaxies. On one side, you have elliptical galaxies with defined structure. As you progress, the galaxies become more stretched out, but still lack definition until suddenly, there’s a bulge in the center and spiral arms! Oh yeah, and then there’s the cousins that no one really likes to hang out with, the “irregular” galaxies, hanging out in the corner.
But there’s another class of galaxies that seems to have fallen off the Hubble wagon. Some spiral galaxies seem to lack defined bulges. These oddities pose a challenge to our understanding of galactic formation.
The current understanding of galactic formation is one of hierarchical merging. Small dwarf galaxies form first, and then form bigger galaxies which merge and continue to eat more dwarf galaxies until a fully fledged galaxy is formed. However, the collisional nature of this formation tends to scatter stars, favoring random orbits towards the center of flattened galaxies, which should create a classical bulge. Galaxies that do not have a bulge, or have a “pseudobulge” (small bulges created by gravitational sorting of stars within an already formed galaxy) don’t seem to fit this picture.
A recent review suggests that galaxies without true bulges are in fact common and include many well-known galaxies such as M101 (the Pinwheel Galaxy) and M33. The team, led by John Kormendy of the University of Texas, Austin, conducted a survey of spiral galaxies in the Local Group to determine just how common they were. To determine the status of the bulge, the team analyzed the physical size of the bulge, its luminosity as a fraction of the overall light output, and the color/age of the stars therein. Bulges that were small, indistinct, and contained stars similar to the color/age of the stars found in the disk were considered examples of the psuedobulges. Ones with significant, bright, and distinctly redder/older bulges were indicative of what would be expected in the classical merger bulge.
The team determined that as much as 58-74% of their sample did not contain a classical bulge. Furthermore, they state, “Almost all of the classical bulges that we do identify – some with substantial uncertainty – are smaller than those normally made in simulations of galaxy formation.” Indeed, included among these galaxies is our own Milky Way which has a very odd, box shaped bulge. The team notes that the velocity distribution of the apparent bulge merges seamlessly into the disk portion of the galaxy as opposed to a discontinuous fit in classical bulges.
Kormendy’s team finds that one way to form such “pure-disk” galaxies is to allow for the possibility of early star formation. According to the paper, this would “give the halo time to grow without forming a classical bulge.”
These findings stand in strong contrast with a study published by the same group in 2009, analyzing the Virgo cluster of galaxies. In that study they found that classical bulge galaxies (including in this study, elliptical galaxies) seemed to dominate. As such, they suggest that the formation of bulges is somehow related to the local environment. Although the question cannot yet be answered, it begs the question for future study: What about our environment is so special that we can form galaxies in a non-merger process? The answer to this question will require further study.
An aurora seen over the South Pole, from the ISS. Credit: Doug Wheelock, NASA.
For many people around the world the ability to see the Aurora Borealis or Aurora Australis is a rare treat. Unless you live north of 60° latitude (or south of -60°), or who have made the trip to tip of Chile or the Arctic Circle at least once in their lives, these fantastic light shows are something you’ve likely only read about or seen a video of.
But on occasion, the “northern” and “southern lights” have reached beyond the Arctic and Antarctic Circles and dazzled people with their stunning luminescence. But what exactly are they? To put it simply, auroras are natural light displays that take place in the night sky, particularly in the Polar Regions, and which are the result of interaction in the ionosphere between the sun’s rays and Earth’s magnetic field.
Description:
Basically, solar wind is periodically launched by the sun which contains clouds of plasma, charged particles that include electrons and positive ions. When they reach the Earth, they interact with the Earth’s magnetic field, which excites oxygen and nitrogen in the Earth’s upper atmosphere. During this process, ionized nitrogen atoms regain an electron, and oxygen and nitrogen atoms return from an excited state to ground state.
High-speed particles from the Sun, mostly electrons, strike oxygen and nitrogen atoms in Earth’s upper atmosphere. Credit: NASA
Excitation energy is lost by the emission of a photon of light, or by collision with another atom or molecule. Different gases produce different colors of light – light emissions coming from oxygen atoms as they interact with solar radiation appear green or brownish-red, while the interaction of nitrogen atoms cause light to be emitted that appears blue or red.
This dancing display of colors is what gives the Aurora its renowned beauty and sense of mystery. In northern latitudes, the effect is known as the Aurora Borealis, named after the Roman Goddess of the dawn (Aurora) and the Greek name for the north wind (Boreas). It was the French scientist Pierre Gassendi who gave them this name after first seeing them in 1621.
In the southern latitudes, it is known as Aurora Australis, Australis being the Latin word for “of the south”. Auroras seen near the magnetic pole may be high overhead, but from farther away, they illuminate the northern horizon as a greenish glow or sometimes a faint red. The auroras are usually best seen in the Arctic and Antarctic because that is the location of the poles of the Earth’s magnetic field.
The South Pole Telescope under the aurora australis (southern lights). Credit: Keith Vanderlinde
Names and Cultural Significance:
The northern lights have had a number of names throughout history and a great deal of significance to a number of cultures. The Cree call this phenomenon the “Dance of the Spirits”, believing that the effect signaled the return of their ancestors.
To the Inuit, it was believed that the spirits were those of animals. Some even believed that as the auroras danced closer to those who were watching them, that they would be enveloped and taken away to the heavens. In Europe, in the Middle Ages, the auroras were commonly believed to be a sign from God.
According to the Norwegian chronicle Konungs Skuggsjá (ca. 1230 CE), the first encounter of the norðrljós (Old Norse for “northern light”) amongst the Norsemen came from Vikings returning from Greenland. The chronicler gives three possible explanations for this phenomena, which included the ocean being surrounded by vast fires, that the sun flares reached around the world to its night side, or that the glaciers could store energy so that they eventually glowed a fluorescent color.
Auroras on Other Planets:
However, Earth is not the only planet in the Solar System that experiences this phenomena. They have been spotted on other Solar planets, and are most visible closer to the poles due to the longer periods of darkness and the magnetic field.
Image of Saturn’s aurora taken by the Huddle Space Telescope and seen in ultraviolet wavelengths. Credit: ESA/NASA/Hubble
For example. the Hubble Space Telescope has observed auroras on both Jupiter and Saturn – both of which have magnetic fields much stronger than Earth’s and extensive radiation belts. Uranus and Neptune have also been observed to have auroras which, same as Earth, appear to be powered by solar wind.
Auroras also have been observed on the surfaces of Io, Europa, and Ganymede using the Hubble Space Telescope, not to mention Venus and Mars. Because Venus has no planetary magnetic field, Venusian auroras appear as bright and diffuse patches of varying shape and intensity, sometimes distributed across the full planetary disc.
An aurora was also detected on Mars on August 14th, 2004, by the SPICAM instrument aboard Mars Express. This aurora was located at Terra Cimmeria, in the region of 177° East, 52° South, and was estimated to be quite sizable – 30 km across and 8 km high (18.5 miles across and 5 miles high).
Mars has magnetized rocks in its crust that create localized, patchy magnetic fields (left). In the illustration at right, we see how those fields extend into space above the rocks. At their tops, auroras can form. Credit: NASA
Though Mars has little magnetosphere to speak of, scientists determined that the region of the emissions corresponded to an area where the strongest magnetic field is localized on the planet. This they concluded by analyzing a map of crustal magnetic anomalies compiled with data from Mars Global Surveyor.
More recently, an aurora was observed on Mars by the MAVEN mission, which captured images of the event on March 17th, 2015, just a day after an aurora was observed here on Earth. Nicknamed Mars’ “Christmas lights”, they were observed across the planet’s mid-northern latitudes and (owing to the lack of oxygen and nitrogen in Mars’ atmosphere) were likely a faint glow compared to Earth’s more vibrant display.
In short, it seems that auroras are destined to happen wherever solar winds and magnetic fields coincide. But somehow, knowing this does not make them any less impressive, or diminish the power they have to inspire wonder and amazement in all those that behold them.
If you’re looking to while away a Friday afternoon in Vancouver, check out this lecture going on at the Rio Theatre on September 17th, 2010 at 12:00pm. There’s going to be an all-star group of lecturers, including Jeremy Heyl, Gaelen Marsden from the BLAST mission, and Dr. Jaymie Matthews, principle investigator with Canada’s MOST Space Telescope.
There are tickets for sale, but the organizer has agreed to let 50 Universe Today readers in for FREE. If you live in the Vancouver, BC area, just email the organizer at i[email protected] and let them know you’d like a free ticket.
Look! Up in the sky! Is it a bird? Is it a plane? No… It’s super Jupiter! “Jupiter is always bright, but if you think it looks a little brighter than usual this month, you’re right,” says Robert Naeye, editor in chief of Sky & Telescope magazine. “Jupiter is making its closest pass by Earth for the year. And this year’s pass is a little closer than any other between 1963 and 2022.”
Where do you find Jupiter? Try about 368 million miles away and (for most observers) low to the southeast after the skies get dark. The giant planet will reach its nearest point to us on the evening of September 20, 2010 – but will remain one of the brightest objects in the night through the end of the month.
Why does Jupiter appear to be more luminous now than at any other time? Although the varying distances over the years may seem marginal – about 10 to 11 million miles over a period of around 60 years – it translates into significance when it comes to magnitude factors. At its brightest, Jupiter can reach –2.94, and dimmest at -1.6. Just a 1% distance change can mean either 4% brighter or dimmer!
The mighty Jove has also undergone some cosmetic changes in the past year as well, making it an additional 4% brighter than usual.
For nearly a year the giant planet’s South Equatorial Belt has slowly been covered by a highly reflective ammonia cloud. Normally the SEB appears to be brown, a result of Jupiter’s chemical compounds reacting to the Sun’s ultraviolet light. Known as “chromophores”, these chemicals are known to mix with lower cloud decks and just a few stormy days could mean rising convection cells are forming crystallized ammonia – masking the light absorbing dark zone and adding to reflectivity.
Of course, a close pass doesn’t mean Jupiter is going to appear to be the size of the Moon – nor be as bright – but it’s certainly going to make a grand appearance on the nights of September 22 and September 23 when it joins Selene on the celestial scene!
But that’s not all that’s happening here. According the Sky & Telescope Magazine: Jupiter and Uranus find themselves close to the point on the sky known as the vernal equinox, where the Sun crosses the celestial equator on the first day of spring. (“Spring” here means spring in the Northern Hemisphere.) And, all of this takes place around the date when fall begins in the
Northern Hemisphere: on September 22nd. (Fall begins at 11:09 p.m. Eastern Daylight Time on that date.)
What do all these coincidences mean? “Nothing at all,” says Alan MacRobert, a senior editor at Sky & Telescope. “People forget that lots of things are going on in the sky all the time. Any particular arrangement might not happen again for centuries, but like the saying goes, there’s always something. Enjoy the show.”
A daytime shot of the Star Field for the 2010 Iowa Star Party held at Whiterock Observatory. 36 participants showed up to take in the incredibly dark skies. Image Credit: Andrew Sorenson
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If you’ve been wanting to get out to view the skies at night from your back yard – or maybe a darker location – but don’t know your way around the skies or have access to a telescope or binoculars, attending a star party may be just what you need to do. I recently attended the 8th annual Iowa Star Party under the dark skies of Coon Rapids, Iowa.
It was an extraordinary experience to meet other amateur astronomers, look at (and through) their telescopes, and in general to be surrounded by a bunch of other people keenly interested in astronomy. Here’s a brief synopsis of what my experience at the star party was like, followed by reasons to seek out a dark-sky gathering near you and a few links to large star parties around the world.
The star party ran from Thursday, September 2nd through Sunday the 5th. In attendance over the weekend were 36 participants and their families, most from Iowa but a few from Minnesota, Nebraska and Illinois. It’s no Astrofest, but it was a good showing for Iowa!
The Iowa Star Party is located at the Whiterock Conservancy, an non-profit land-trust that is gracious enough to host the party every year, and has named the field in which the ‘scopes are located the Star Field. The site was chosen by former Ames Area Amateur Astronomers member Dave Oesper because it is the least populated place with the lowest amount of light pollution in central Iowa. The Ames club, of which I am a member, did much of the organizing for the event. All three nights were perfectly clear with good seeing, and though it was really windy during the daytime, it tended to calm down towards the evening.
I was not personally able to attend the first evening, but it was reportedly cold and clear, and the few that did show up for the kickoff were treated to dark, clear skies and little wind. Friday was the public night, where anyone from anywhere was invited to come look through a scope and attend a talk about the history of astronomy and some general information about viewing by local amateur astronomer Drew Sorenson.
The talk ended in a “debate” about refractors vs. reflectors that turned out to be a surprise, unplanned marshmallow fight. Yeah, we threw marshmallows at each other – with gusto I might add. A 60mm homemade refractor was then raffled off as a door prize.
175 members of the public showed up for a short presentation and a long night of good viewing on Friday at the Iowa Star Party. Facing the camera at the table are Emily Babbin of Whitrock Conservancy, center, and Al Johnson, Vice President of the AAAA, right. Image Credit: Andrew Sorenson
In all, 175 people showed up for what turned out to be a spectacular night under some of the darkest skies I’ve seen. Members of the public were treated to a spectacular view of the Milky Way, as well as views of Jupiter, M13, Mizar, Albirio, and countless other objects through the eyepieces of about 20 telescopes.
Saturday night, the last evening of the star party, there was a banquet followed by a talk by Dr. Charles Nelson, Drake University Assistant Professor of Astronomy. Dr. Nelson gave a talk about quasars, which included a brief history of their discovery and the techniques we use to study and analyze them today, with a heavy emphasis on spectroscopy. After the talk, everyone headed out to the Star Field to spend the rest of the dark night observing.
Objects that my club viewed included the Veil Nebula (which was stunningly large and wispy through my club’s 24″ telescope), Herschel’s Garnet, the Whirlpool Galaxy, the Andromeda Galaxy, M31, M22 and Jupiter and Uranus. Other participants viewed the quasar Markarian 205, in keeping with the quasar-themed lecture.
We concluded Sunday with a breakfast, during which I made countless pancakes faster than I’ve ever made pancakes before. Staying up all night staring at the stars makes one hungry!
This is just a small taste of my own individual experience, but all of this fun and more could be had by you! Here are a few reasons to seek out your own star party:
– You might will learn something – No matter how much time you spend at a ‘scope, meeting with other amateur astronomers will give you ideas and techniques and knowledge that you couldn’t even dream of discovering on your own. Plus, it’s fun to share an interest in any subject with other human beings, face to face.
– You’ll see more than you would at home – Larger star parties are inherently located in areas with very dark skies, meaning that there will be so much more to see than you could at home. Even smaller star parties near towns tend to avoid locations that are polluted by city lights. Plus, there will likely be people there with huge telescopes that are more than willing to show you all that a large light bucket has to offer. – You can share your knowledge of the skies – A star party is a great chance to show off your knowledge of the skies to other amateurs, as well as members of the public if there is a public viewing night.
– You will meet other astronomers – Sure, amateur astronomy can be a lonely hobby, spending hours outside in the dark when everyone else is asleep. But at a star party, you’ll get the chance to share your passion for the skies with other astronomers, look through their telescopes and show them your own. You’re not alone!
-You’ll have fun – Even if you have a passing interest in astronomy and/or don’t own a telescope or binoculars, looking through a telescope is just plain cool, and getting to know your way around the skies is always a treat. And if it clouds over, chances are that someone will bring old episodes of Star Trek to watch!
If you’re interested in finding your nearest star party, here are a few resources to take a look at.
In the United States, The Astronomical League compiles a list of upcoming star parties and astronomy-related events on their website and in their print newsletter, The Reflector.
Of course, this only covers our readership located in the predominantly English-speaking regions of the Earth, so if you have a favorite event near you, feel free to link to it in the comments. Also share your favorite memory of a star party in the comments section, if you feel moved to do so.
As amateur astronomers are wont to say, “Clear Skies!”
Illustration of the dipolar variation in the fine-structure constant, alpha, across the sky, as seen by the two telescopes used in the work: the Keck telescope in Hawaii and the ESO Very Large Telescope in Chile. IMAGE CREDIT: Copyright Dr. Julian Berengut, UNSW, 2010.
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In order for astronomers to explore the outer reaches of our universe, they rely upon the assumption that the physical constants we observe in the lab on Earth are physically constant everywhere in the universe. This assumption seems to hold up extremely well. If the universe’s constants were grossly different, stars would fail to shine and galaxies would fail to coalesce. Yet as far we we look in our universe, the effects which rely on these physical constants being constant, still seem to happen. But new research has revealed that one of these constants, known as the fine structure constant, may vary ever so slightly in different portions of the universe.
Of all physical constants, the fine structure constant seems like an odd one to be probing with astronomy. It appears in many equations involving some of the smallest scales in the universe. In particular, it is used frequently in quantum physics and is part of the quantum derivation of the structure of the hydrogen atom. This quantum model determines the allowed energy levels of electrons in the atoms. Change this constant and the orbitals shift as well.
Since the allowed energy levels determine what wavelengths of light such an atom can emit, a careful analysis of the positioning of these spectral lines in distant galaxies would reveal variations in the constant that helped control them. Using the Very Large Telescope (VLT) and the Keck Observatory, a team from the University of New South Whales has analyzed the spectra of 300 galaxies and found the subtle changes that should exist if this constant was less than constant.
Since the two sets of telescopes used point in different directions (Keck in the Northern hemisphere and the VLT in the Southern), the researchers noticed that the variation seemed to have a preferred direction. As Julian King, one of the paper’s authors, explained, “Looking to the north with Keck we see, on average, a smaller alpha in distant galaxies, but when looking south with the VLT we see a larger alpha.”
However, “it varies by only a tiny amount — about one part in 100,000 — over most of the observable universe”. As such, although the result is very intriguing, it does not demolish our understanding of the universe or make hypotheses like that of a greatly variable speed of light plausible (an argument frequently tossed around by Creationists). But, “If our results are correct, clearly we shall need new physical theories to satisfactorily describe them.”
While this finding doesn’t challenge our knowledge of the observable universe, it may have implications for regions outside of the portion of the universe we can observe. Since our viewing distance is ultimately limited by how far we can look back, and that time is limited by when the universe became transparent, we cannot observe what the universe would be like beyond that visible horizon. The team speculates that beyond it, there may be even larger changes in this constant which would have large effects on physics in such portions. They conclude the results may, “suggest a violation of the Einstein Equivalence Principle, and could infer a very large or in finite universe, within which our `local’ Hubble volume represents a tiny fraction, with correspondingly small variations in the physical constants.”
This would mean that, outside of our portion of the universe, the physical laws may not be suitable for life making our little corner of the universe a sort of oasis. This could help solve the supposed “fine-tuning” problem without relying on explanations such as multiple universes.
Want some other articles on this subject? Here’s an article about there might be 10 dimensions.
Smaller satellite galaxies caught by a spiral galaxy are distorted into elongated structures consisting of stars, which are known as tidal streams, as shown in this artist's impression. Credit: Jon Lomberg
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On Friday, I wrote about the population of the thick disk and how surveys are revealing that this portion of our galaxy is largely made of stars stolen from cannibalized dwarf galaxies. This fits in well with many other pieces of evidence to build up the general picture of galactic formation that suggests galaxies form through the combination of many small additions as opposed to a single, gigantic collapse. While many streams of what is, presumably, tidally shredded galaxies span the outskirts of the Milky Way, and other objects exist that are still fully formed galaxies, few objects have yet been identified as a satellite that is undergoing the process of tidal disruption.
A new study, to be published in the October issue of the Astrophysical Journal suggests that the Hercules satellite galaxy may be one of the first of this intermediary forms discovered.
In the past decade, numerous minor stellar systems have been discovered in the halo of our Milky Way galaxy. The properties of these systems have suggested to astronomers that they are faint galaxies in their own right. Although many have elongated and elliptical shapes (averaging an ellipticity of 0.47; 0.15 higher than that of brighter dwarf galaxies that orbit further out), simulations have suggested that even these stretched dwarfs are still able to remain largely cohesive. In general, the galaxy will remain intact until it is stretched to an ellipticity of 0.7. At this point, a minor galaxy will lose ~90% of its member stars and dissolve into a stellar stream.
In 2008, Munoz et al. reported the first Milky Way satellite that was clearly over this limit. The Ursa Major I satellite was shown to have an ellipticity of 0.8. Munoz suggested that this, as well as the Hercules and Ursa Major II dwarfs were undergoing tidal break up.
The new paper, by Nicolas Martin and Shoko Jin, further analyzes this proposition for the Hercules satellite by going further and examining the orbital characteristics to ensure that their passage would continue to distort the galaxy sufficiently. The system already contains an ellipticity of 0.68, which puts it just under the theoretical limit.
The team looked to see just how closely the satellite would pass to our own galactic center. The closer it passed, the more disruption it would feel. By projecting the orbit, they estimated the galaxy would come within ~6 kiloparsecs of the galactic center which is about 40% of the radius of the galaxy overall. While this may not seem especially close Martin and Jin report that they cannot conclude that it will be insufficient. They state that disruption would be dependent on “the properties of the stellar system at that time of its journey in the Milky Way potential and, as such, out of reach to the current observer.”
However, there were some telling signs that the dwarf may already be shedding stars. Along the major axis of the galaxy, deep imaging has revealed a smaller number of stars that does not appear to be bound to the galaxy itself. Photometry of these stars has shown that their distribution on a color-magnitude diagram is strikingly similar to that of the Hercules galaxy itself.
At this point, we cannot fully determine if the Hercules galaxy is doomed to become another stellar stream around the Milky Way, but if it is not truly in the process of breaking up, it seems to be on the very edge.
Labelled version of the Planck space observatory's all-sky survey. Credit: ESA.
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Remember how you could once pick up a book about the first three minutes after the Big Bang and be amazed by the level of detail that observation and theory could provide regarding those early moments of the universe. These days the focus is more on what happened between 1×10-36 and 1×10-32 of the first second as we try to marry theory with more detailed observations of the cosmic microwave background.
About 380,000 years after the Big Bang, the early universe became cool and diffuse enough for light to move unimpeded, which it proceeded to do – carrying with it information about the ‘surface of last scattering’. Before this time photons were being continually absorbed and re-emitted (i.e. scattered) by the hot dense plasma of the earlier universe – and never really got going anywhere as light rays.
But quite suddenly, the universe got a lot less crowded when it cooled enough for electrons to combine with nuclei to form the first atoms. So this first burst of light, as the universe became suddenly transparent to radiation, contained photons emitted in that fairly singular moment – since the circumstances to enable such a universal burst of energy only happened once.
With the expansion of the universe over a further 13.6 and a bit billion years, lots of these photons probably crashed into something long ago, but enough are still left over to fill the sky with a signature energy burst that might have once been powerful gamma rays but has now been stretched right out into microwave. Nonetheless, it still contains that same ‘surface of last scattering’ information.
Observations tell us that, at a certain level, the cosmic microwave background is remarkably isotropic. This led to the cosmic inflation theory, where we think there was a very early exponential expansion of the microscopic universe at around 1×10-36 of the first second – which explains why everything appears so evenly spread out.
Really, the most remarkable thing about the CMB is its large scale isotropy and finding some fine grain anisotropies is perhaps not that surprising. However, it is data and it gives theorists something from which to build mathematical models about the contents of the early universe.
The apparent quadrupole moment anomalies in the cosmic microwave background might result from irregularities in the early universe - including density fluctuations, dynamic movement (vorticity) or even gravity waves. However, a degree of uncertainty and 'noise' from foreground light sources is apparent in the data, making firm conclusions difficult to draw. Credit: University of Chicago.
Some theorists speak of CMB quadrupole moment anomalies. The quadrupole idea is essentially an expression of energy density distribution within a spherical volume – which might scatter light up-down or back-forward (or variations from those four ‘polar’ directions). A degree of variable deflection from the surface of last scattering then hints at anisotropies in the spherical volume that represents the early universe.
For example, say it was filled with mini black holes (MBHs)? Scardigli et al (see below) mathematically investigated three scenarios, where just prior to cosmic inflation at 1×10-36 seconds: 1) the tiny primeval universe was filled with a collection of MBHs; 2) the same MBHs immediately evaporated, creating multiple point sources of Hawking radiation; or 3) there were no MBHs, in accordance with conventional theory.
When they ran the math, scenario 1 best fits with WMAP observations of anomalous quadrupole anisotropies. So, hey – why not? A tiny proto-universe filled with mini black holes. It’s another option to test when some higher resolution CMB data comes in from Planck or other future missions to come. And in the meantime, it’s material for an astronomy writer desperate for a story.
