The Hercules Satellite – A Galactic Transitional Fossil

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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.

The Thick Disk: Galactic Construction Project or Galactic Rejects?

Our Milky Way Gets a Makeover

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The disk of spiral galaxies is comprised of two main components: The thin disk holds the majority of stars and gas and is the majority of what we see and picture when we think of spiral galaxies. However, hovering around that, is a thicker disk of stars that is much less populated. This thick disk is distinct from the thin disk in several regards: The stars there tend to be older, metal deficient, and orbit the center of the galaxy more slowly.

But where this population of the stars came from has been a long standing mystery since its identification in the mid 1970’s. One hypothesis is that it is the remainder of cannibalized dwarf galaxies that have never settled into a more standard orbit. Others suggest that these stars have been flung from the thin disk through gravitational slingshots or supernovae. A recent paper puts these hypothesis to the observational test.

At a first glance, both propositions seem to have a firm observational footing. The Milky Way galaxy is known to be in the process of merging with several smaller galaxies. As our galaxy pulls them in, the tidal effects shred these minor galaxies, scattering the stars. Numerous tidal streams of this sort have been discovered already. The ejection from the thin disk gains support from the many known “runaway” and “hypervelocity” stars which have sufficient velocity to escape the thin disk, and in some cases, the galaxy itself.

The new study, led by Marion Dierickx of Harvard, follows up on a 2009 study by Sales et al., which used simulations to examine the features stars would take in the thick disk should they be created via these methods. Through these simulations, Sales showed that the distribution of eccentricities of the orbits should be different and allow a method by which to discriminate between formation scenarios.

By using data from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), Dierickx’s team compared the distribution of the stars in our own galaxy to the predictions made by the various models. Ultimately, their survey included some 34,000 stars. By comparing the histogram of eccentricities to that of Sales’ predictions, the team hoped to find a suitable match that would reveal the primary mode of creation.

The comparison revealed that, should ejection from the thin disk be the norm there were too many stars in nearly circular orbits as well as highly eccentric ones. In general, the distribution was too wide. However, the match for the scenario of mergers fit well lending strong credence to this hypothesis.

While the ejection hypothesis or others can’t be ruled out completely, it suggests that, at least in our own galaxy, they play a rather minor role. In the future, additional tests will likely be employed, analyzing other aspects of this population.

Finding the Origin of Milky Way’s Ancient Stars

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From the Royal Astronomical Society

Many of the Milky Way’s ancient stars are remnants of other smaller galaxies torn apart by violent galactic collisions around five billion years ago, according to researchers at Durham University, who publish their results in a new paper in the journal Monthly Notices of the Royal Astronomical Society.

Scientists at Durham’s Institute for Computational Cosmology and their collaborators at the Max Planck Institute for Astrophysics, in Germany, and Groningen University, in Holland, ran huge computer simulations to recreate the beginnings of our Galaxy.

The simulations revealed that the ancient stars, found in a stellar halo of debris surrounding the Milky Way, had been ripped from smaller galaxies by the gravitational forces generated by colliding galaxies.

Cosmologists predict that the early Universe was full of small galaxies which led short and violent lives. These galaxies collided with each other leaving behind debris which eventually settled into more familiar looking galaxies like the Milky Way.

The researchers say their finding supports the theory that many of the Milky Way’s ancient stars had once belonged to other galaxies instead of being the earliest stars born inside the Galaxy when it began to form about 10 billion years ago.

Simulation showing the stellar halo of a Milky Way-like galaxy in the present day. Credit: Andrew Cooper (Durham University)

Lead author Andrew Cooper, from Durham University’s Institute for Computational Cosmology, said: “Effectively we became galactic archaeologists, hunting out the likely sites where ancient stars could be scattered around the galaxy.

“Our simulations show how different relics in the Galaxy today, like these ancient stars, are related to events in the distant past.

“Like ancient rock strata that reveal the history of Earth, the stellar halo preserves a record of a dramatic primeval period in the life of the Milky Way which ended long before the Sun was born.”

The computer simulations started from shortly after the Big Bang, around 13 billion years ago, and used the universal laws of physics to simulate the evolution of dark matter and the stars.

These simulations are the most realistic to date, capable of zooming into the very fine detail of the stellar halo structure, including star “streams” – which are stars being pulled from the smaller galaxies by the gravity of the dark matter.

One in one hundred stars in the Milky Way belong to the stellar halo, which is much larger than the Galaxy’s familiar spiral disk. These stars are almost as old as the Universe.

Professor Carlos Frenk, Director of Durham University’s Institute for Computational Cosmology, said: “The simulations are a blueprint for galaxy formation.

“They show that vital clues to the early, violent history of the Milky Way lie on our galactic doorstep.

“Our data will help observers decode the trials and tribulations of our Galaxy in a similar way to how archaeologists work out how ancient Romans lived from the artefacts they left behind.”

The research is part of the Aquarius Project, which uses the largest supercomputer simulations to study the formation of galaxies like the Milky Way and was partly funded by the UK’s Science and Technology Facilities Council (STFC).

Aquarius was carried out by the Virgo Consortium, involving scientists from the Max Planck Institute for Astrophysics in Germany, the Institute for Computational Cosmology at Durham University, UK, the University of Victoria in Canada, the University of Groningen in the Netherlands, Caltech in the USA and Trieste in Italy.

Durham’s cosmologists will present their work to the public as part of the Royal Society’s 350th anniversary ‘See Further’ exhibition, held at London’s Southbank Centre until July 4th.

Planck Reveals Giant Dust Structures in our Local Neighborhood

This new image from Planck spans about 50° of the sky. Credits: ESA/HFI Consortium/IRAS

Dust has never looked so beautiful! This new image from the Planck spacecraft shows giant filaments of cold dust stretching through our galaxy. The image spans about 50 degrees of the sky, showing our local neighborhood within approximately 500 light-years of the Sun. “What makes these structures have these particular shapes is not well understood,” says Jan Tauber, ESA Project Scientist for Planck. Analyzing these structures could help to determine the forces that shape our galaxy and trigger star formation.
Continue reading “Planck Reveals Giant Dust Structures in our Local Neighborhood”

Second-Generation Star Supports Cannibal Theory of Milky Way

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A newly discovered red giant star is a relic from the early universe — a star that may have been among the second generation of stars to form after the Big Bang. Located in the dwarf galaxy Sculptor some 290,000 light-years away, the star has a remarkably similar chemical make-up to the Milky Way’s oldest stars. Its presence supports the theory that our galaxy underwent a “cannibal” phase, growing to its current size by swallowing dwarf galaxies and other galactic building blocks.

“This star likely is almost as old as the universe itself,” said astronomer Anna Frebel of the Harvard-Smithsonian Center for Astrophysics, lead author of the Nature paper reporting the finding.

Dwarf galaxies are small galaxies with just a few billion stars, compared to hundreds of billions in the Milky Way. In the “bottom-up model” of galaxy formation, large galaxies attained their size over
billions of years by absorbing their smaller neighbors.

“If you watched a time-lapse movie of our galaxy, you would see a swarm of dwarf galaxies buzzing around it like bees around a beehive,” explained Frebel. “Over time, those galaxies smashed together and mingled their stars to make one large galaxy — the Milky Way.”

If dwarf galaxies are indeed the building blocks of larger galaxies, then the same kinds of stars should be found in both kinds of galaxies, especially in the case of old, “metal-poor” stars. To astronomers, “metals” are chemical elements heavier than hydrogen or helium. Because they are products of stellar evolution, metals were rare in the early Universe, and so old stars tend to be metal-poor.

Old stars in the Milky Way’s halo can be extremely metal-poor, with metal abundances 100,000 times poorer than in the Sun, which is a typical younger, metal-rich star. Surveys over the past decade have
failed to turn up any such extremely metal-poor stars in dwarf galaxies, however.

“The Milky Way seemed to have stars that were much more primitive than any of the stars in any of the dwarf galaxies,” says co-author Josh Simon of the Observatories of the Carnegie Institution. “If dwarf
galaxies were the original components of the Milky Way, then it’s hard to understand why they wouldn’t have similar stars.”

The team suspected that the methods used to find metal-poor stars in dwarf galaxies were biased in a way that caused the surveys to miss the most metal-poor stars. Team member Evan Kirby, a Caltech
astronomer, developed a method to estimate the metal abundances of large numbers of stars at a time, making it possible to efficiently search for the most metal-poor stars in dwarf galaxies.

“This was harder than finding a needle in a haystack. We needed to find a needle in a stack of needles,” said Kirby. “We sorted through hundreds of candidates to find our target.”

Among stars he found in the Sculptor dwarf galaxy was one faint, 18th-magnitude speck designated S1020549. Spectroscopic measurements of the star’s light with Carnegie’s Magellan-Clay telescope in Las Campanas, Chile, determined it to have a metal abundance 6,000 times lower than that of the Sun; this is five times lower than any other star found so far in a dwarf galaxy.

The researchers measured S1020549’s total metal abundance from elements such as magnesium, calcium, titanium, and iron. The overall abundance pattern resembles those of old Milky Way stars, lending the first observational support to the idea that these galactic stars originally formed in dwarf galaxies.

The researchers expect that further searches will discover additional metal-poor stars in dwarf galaxies, although the distance and faintness of the stars pose a challenge for current optical telescopes. The next generation of extremely large optical telescopes, such as the proposed 24.5-meter Giant Magellan Telescope, equipped with high-resolution spectrographs, will open up a new window for studying the growth of galaxies through the chemistries of their stars.

In the meantime, says Simon, the extremely low metal abundance in S1020549 study marks a significant step towards understanding how our galaxy was assembled. “The original idea that the halo of the Milky
Way was formed by destroying a lot of dwarf galaxies does indeed appear to be correct.”

Source: Harvard-Smithsonian Center for Astrophysics

Alien Star Clusters Are Invading the Milky Way

Globular Cluster

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We’re being invaded! About one-fourth of the star clusters in our galaxy are actually invaders from other galaxies, according to a new paper. Research from a team of scientists from Swinburne University of Technology in Australia shows that that many of our galaxy’s globular star clusters are actually foreigners – having been born elsewhere and then migrated to our Milky Way. “It turns out that many of the stars and globular star clusters we see when we look into the night sky are not natives, but aliens from other galaxies,” said Duncan Forbes. “They have made their way into our galaxy over the last few billion years.”

Previously astronomers had suspected that some globular star clusters, which each contain between 10000 and several million stars were foreign to our galaxy, but it was difficult to positively identify which ones.

Using Hubble Space Telescope data, Forbes, along with his Canadian colleague Professor Terry Bridges, examined globular star clusters within the Milky Way galaxy.

They then compiled the largest ever high-quality database to record the age and chemical properties of each of these clusters.

“Using this database we were able to identify key signatures in many of the globular star clusters that gave us tell-tale clues as to their external origin,” Forbes said.

“We determined that these foreign-born globular star clusters actually make up about one quarter of our Milky Way globular star cluster system. That implies tens of millions of accreted stars – those that have joined and grown our galaxy – from globular star clusters alone.”

The researchers’ work also suggests that the Milky Way may have swallowed up more dwarf galaxies than was previously thought.

“We found that many of the foreign clusters originally existed within dwarf galaxies – that is ‘mini’ galaxies of up to 100 million stars that sit within our larger Milky Way,” said Forbes. “Our work shows that there are more of these accreted dwarf galaxies in our Milky Way than was thought. Astronomers had been able to confirm the existence of two accreted dwarf galaxies in our Milky Way – but our research suggests that there might be as many as six yet to be discovered.”

“Although the dwarf galaxies are broken-up and their stars assimilated into the Milky Way, the globular star clusters of the dwarf galaxy remain intact and survive the accretion process,” Forbes continued. “This will have to be explored further, but it is a very exciting prospect that will help us to better understand the history of our own galaxy.”

Read the team’s paper.
Source: Royal Astronomical Society

Astronomy Without A Telescope – Don’t Make a Meal of It

You should always put out the old dinner set when you have astronomers around. It all starts innocently enough with imagine this wineglass is the Earth rotating on its axis… But then someone decides that large plate is just right to show the orientation of an orbital plane and more wine glasses are brought to bear to test a solution to the three body problem and…

My favorite dinner set demonstration is to use the whole table to represent the galactic plane – ideally with an upturned wide rimmed soup bowl in the middle to mimic the galactic hub. Then you get a plate to represent the solar system’s orbital plane and hold it roughly facing the galactic hub, but at a 63 degree angle from the horizontal. We know the equatorial plane of the Milky Way is tilted 63 degrees from the ecliptic – or vice versa since here we are arbitrarily making the galactic plane (table) the horizontal. This means galactic north is up towards the ceiling – and incidentally a line drawn north up from the galaxy’s centre (i.e. the galactic axis) passes fairly close to Arcturus.

Now for the Earth. Wine glasses make an excellent Earth model since the stem can represent the Earth’s axis of rotation. The glass is at least a bit round and you can see through it for a view of what someone would see from the surface of that glass.

Looking down on the solar system (plate) from its north, which is orientated away from the galactic hub (table), it actually rotates anti-clockwise. So if you hold the glass at the top of the plate – that’s Earth at about September, then move it to the left for December, down to the bottom for March, right side for June and back to September. 

So, holding your plate at 63 degrees to the table, now hold the wine glass tilted at 23.5 degrees to the plate. Assuming you left your protractor at home – this will mean the wine glass stem is now almost parallel to the table – since 63 + 23.5 is close to 90 degrees. In other words, the Earth’s axis is almost perpendicular to the galactic axis.

The range of different orientations available to you. The axis of Earth's rotation (represented by the 'celestial equator') is almost perpendicular to the orbital plane of the galaxy.

You should really imagine the plate being embedded within the table, since you will always see some part of the Milky Way at night throughout the year. But, in any case, the wine glass gives a good demonstration of why we southerners get such a splendid view of the galactic hub in Sagittarius. It’s hidden in the daytime around March – but come September about 7pm you get the Milky Way running almost north-south across the sky with Sagittarius almost directly overhead. Arcturus is visible just above the western horizon, being about where the galaxy’s northern axis points (that is, the ceiling above the middle of the table).

And if you look to the north you can see Vega just above the horizon – which is more or less the direction the solar system (plate) is heading in its clockwise orbit around the galaxy (table).

Now, what’s really interesting is if I add the Moon in by just, oh… Er, sorry – that wasn’t new was it?

Seven-Year WMAP Results: No, They’re NOT Anomalies

Since the day the first Wilkinson Microwave Anisotropy Probe (WMAP) data were released, in 2003, all manner of cosmic microwave background (CMB) anomalies have been reported; there’s been the cold spot that might be a window into a parallel universe, the “Axis of Evil”, pawprints of local interstellar neutral hydrogen, and much, much more.

But do the WMAP data really, truly, absolutely contain evidence of anomalies, things that just do not fit within the six-parameters-and-a-model the WMAP team recently reported?

In a word, no.

Seven Year Microwave Sky (Credit: NASA/WMAP Science Team)

Every second year since 2003 the WMAP science team has published a set of papers on their analyses of the cumulative data, and their findings (with the mission due to end later this year, their next set will, sadly, be their last). With time and experience – not to mention inputs from the thousands of other researchers who have picked over the data – the team has not only amassed a lot more data, but has also come to understand how WMAP operates far better. As a consequence, not only are the published results – such as limits on the nature of dark energy, and the number of different kinds of neutrinos – more stringent and robust, but the team has also become very au fait with the various anomalies reported.

For the first time, the team has examined these anomalies, in detail, and has concluded that the answer to the question, in their words, “are there potential deviations from ?CDM within the context of the allowed parameter ranges of the existing WMAP observations?” is “no”.

The reported anomalies the team examined are many – two prominent cold spots, strength of the quadrupole, lack of large angular scale CMB power, alignment of the quadrupole and octupole components, hemispherical or dipole power asymmetry, to name but a handful – but the reasons for the apparent anomalies are few.

“Human eyes and brains are excellent at detecting visual patterns, but poor at assessing probabilities. Features seen in the WMAP maps, such as the large Cold Spot I near the Galactic center region, can stand out as unusual. However, the likelihood of such features can not be discerned by visual inspection of our particular realization of the universe,” they write, and “Monte Carlo simulations are an invaluable way to determine the expected deviations within the ?CDM model. Claims of anomalies without Monte Carlo simulations are necessarily weak claims”.

Stephen Hawking’s initials in the CMB (Credit: NASA/WMAP Science Team)

An amusing example: Stephen Hawking’s initials (“SH”) can be clearly seen in the WMAP sky map. “The “S” and “H” are in roughly the same font size and style, and both letters are aligned neatly along a line of fixed Galactic latitude,” the team says; “A calculation would show that the probability of this particular occurrence is vanishingly small. Yet, there is no case to made for a non-standard cosmology despite this extraordinarily low probability event,” they dryly note.

Many of the reports of WMAP CMB anomalies would likely make for good teaching material, as they illustrate well the many traps that you can so easily fall into when doing after-the-fact (a posteriori) statistical analyses. Or, as the team puts it in regard to the Stephen Hawking initials: “It is clear that the combined selection of looking for initials, these particular initials, and their alignment and location are all a posteriori choices. For a rich data set, as is the case with WMAP, there are a lot of data and a lot of ways of analyzing the data.”

And what happens when you have a lot of data? Low probability events are guaranteed to occur! “For example, it is not unexpected to find a 2? feature when analyzing a rich data set in a number of different ways. However, to assess whether a particular 2? feature is interesting, one is often tempted to narrow in on it to isolate its behavior. That process involves a posteriori choices that amplify the apparent significance of the feature.”

So, does the team conclude that all this anomaly hunting is a waste of effort? Absolutely not! I’ll quote from the team’s own conclusion: “The search for oddities in the data is essential for testing the model. The success of the model makes these searches even more important. A detection of any highly significant a posteriori feature could become a serious challenge for the model. The less significant features discussed in this paper provided the motivation for considering alternative models and developing new analysis of WMAP (and soon Planck) data. The oddities have triggered proposed new observations that can further test the models. It is often difficult to assess the statistical claims. It may well be that an oddity could be found that motivates a new theory, which then could be tested as a hypothesis against ?CDM. The data support these comparisons. Of course, other cosmological measurements must also play a role in testing new hypotheses. No CMB anomaly reported to date has caused the scientific community to adopt a new standard model of cosmology, but claimed anomalies have been used to provoke thought and to search for improved theories.”

Primary source: Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Are There Cosmic Microwave Background Anomalies? (arXiv:1001.4758). The five other Seven-Year WMAP papers are: Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation (arXiv:1001.4538), Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Planets and Celestial Calibration Sources (arXiv:1001.4731), Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Sky Maps, Systematic Errors, and Basic Results (arXiv:1001.4744), Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Power Spectra and WMAP-Derived Parameters (arXiv:1001.4635), and Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Galactic Foreground Emission (arXiv:1001.4555). Also check out the official WMAP website.

If the Earth is Rare, We May Not Hear from ET

Earth - Moon System

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If civilization-forming intelligent life is rare in our Milky Way galaxy, chances are we won’t hear from ET before the Sun goes red giant, in about five billion years’ time; however, if we do hear from ET before then, we’ll have lots of nice chats before the Earth is sterilized.

That’s the conclusion from a recent study of Ward and Brownlee’s Rare Earth hypothesis by Duncan Forgan and Ken Rice, in which they made a toy galaxy, simulating the real one we live in, and ran it 30 times. In their toy galaxy, intelligent life formed on Earth-like planets only, just as it does in the Rare Earth hypothesis.

While the Forgan and Rice simulations are still limited and somewhat unrealistic, they give a better handle on SETI’s chances for success than either the Drake equation or Fermi’s “Where are they?”

“The Drake equation itself does suffer from some key weaknesses: it relies strongly on mean estimations of variables such as the star formation rate; it is unable to incorporate the effects of the physico-chemical history of the galaxy, or the time-dependence of its terms,” Forgan says, “Indeed, it is criticized for its polarizing effect on “contact optimists” and “contact pessimists”, who ascribe very different values to the parameters, and return values of the number of galactic civilizations who can communicate with Earth between a hundred-thousandth and a million (!)”

Building on the work of Vukotic and Cirkovic, Forgan developed a Monte Carlo-based simulation of our galaxy; as inputs, he used the best estimates of actual astrophysical parameters such as the star formation rate, initial mass function, a star’s time spent on the main sequence, likelihood of death from the skies, etc. For several key inputs however, “the model goes beyond relatively well-constrained parameters, and becomes hypothesis,” Forgan explains, “In essence, the method generates a Galaxy of a billion stars, each with their own stellar properties (mass, luminosity, location in the Galaxy, etc.) randomly selected from observed statistical distributions. Planetary systems are then generated for these stars in a similar manner, and life is allowed to evolve in these planets according to some hypothesis of origin. The end result is a mock Galaxy which is statistically representative of the Milky Way. To quantify random sampling errors, this process is repeated many times: this allows an estimation of the sample mean and sample standard deviation of the output variables obtained.”

Forgan simulated the Rare Earth hypothesis by allowing animal life – the only kind of life from which intelligent civilizations can arise – to form only if homeworld’s mass is between a half and two Earths, if homesun’s mass is between a half and 1.5 times our Sun’s, homeworld has at least one moon (for tides and axial stability), and if homesun has at least one planet of mass at least ten times that of Earth, in an outer orbit (to cut down on death from the skies due to asteroids and comets).

The good news for SETI is that a galaxy like ours should host hundreds of intelligent civilizations (though, somewhat surprisingly, there is no galactic goldilocks zone); the bad news is that during the time such a civilization could communicate with an ET – between when it becomes technologically advanced enough and when it is wiped out by homesun going red giant – there are, in most simulations, no other such civilizations (or if there are, they are too far away) … we, or ET, would be alone.

But it’s not all bad news; if we are not alone, then once contact is established, we will have many phone calls with ET.

To be sure, this is but a work-in-progress. “Numerical modeling of this type is generally a shadow of the entity it attempts to model, in this case the Milky Way and its constituent stars, planets and other objects,” Forgan and Rice say; several improvements are already being worked on.

Sources: “A numerical testbed for hypotheses of extraterrestrial life and intelligence” (Forgan D., 2009, International Journal of Astrobiology, 8, 121), and “Numerical Testing of The Rare Earth Hypothesis using Monte Carlo Realisation Techniques” (arXiv:1001:1680); this too will be published in IJA, likely in April.

Intergalactic Connection is Older, Longer than Thought

Our galaxy has a streamer, though it’s not like the ones you had on your bike as a kid: this streamer is a flow of largely hydrogen gas that originates in the Large and Small Magellanic Clouds, two of our closest galactic neighbors. New observations of the stream have helped to revise its age and extent, and show it to be longer and much older than previous estimates.

The Magellanic Stream, which was discovered over 30 years ago, flows from the two galaxies closest to the Milky Way, the Large and Small Magellanic Clouds. These clouds, which are actually two irregular dwarf galaxies, are 150,000 to 200,000 light-years away, and are visible in the southern hemisphere.

The stream connects up with the Milky Way about 70,000 light years from the Solar System, in the constellation of the Southern Cross.

Using the Green Bank Telescope (GBT), a team of astronomers took over 100 hours of observations of the streamer. These observations were combined with those from other radio telescopes, including the Aricebo telescope in Puerto Rico, to further constrain both its extent and age.

Their observations were presented at the American Astronomical Society’s meeting in Washington D.C., and a paper has been submitted to the Astrophysical Journal. The team included David Nidever and Steven Majewski of the Department of Astronomy at the University of Virginia, Butler Burton of the Leiden Observatory and the National Radio Astronomy Observatory and Lou Nigra of the University of Wisconsin.

Previous observations of the stream showed it to have gaps between the Magellanic Clouds and where it enters the Milky Way, but these revised observations show it to be one continuous stream between the three galaxies. The stream is also at least forty percent longer that previously estimated.

The Magellanic Stream was also determined by the astronomers to be much older than had been estimated before: up from 1.75 billion years old to 2.5 billion years old. Just how does this long-lived intergalactic trail of hydrogen crumbs start off in the Magellanic Clouds?

“The new age of the stream puts its beginning at about the time when the two Magellanic Clouds may have passed close to each other, triggering massive bursts of star formation. The strong stellar winds and supernova explosions from that burst of star formation could have blown out the gas and started it flowing toward the Milky Way,” said David Nidever in a NRAO press release.

By getting a better picture of how the gas flows from the Magellanic Clouds into the Milky Way, astronomers have been able to determine with better accuracy just how far away the two galaxies are, as well as their  interactions with the tidal forces of the Milky Way.

This team has collaborated before on the exploration of the Magellanic Stream and its origins. You can read about their previous findings on Arxiv right here, which were also published in the Astrophysical Journal.

Source: NRAO press release