Can Stars Collide?

Can Stars Collide?

Imagine a really bad day. Perhaps you’re imagining a day where the Sun crashes into another star, destroying most of the Solar System.

No? Well then, even in your imagination things aren’t so bad… It’s all just matter of perspective.

Fortunately for us, we live in out the boring suburbs of the Milky Way. Out here, distances between stars are so vast that collisions are incredibly rare. There are places in the Milky Way where stars are crowded more densely, like globular clusters, and we get to see the aftermath of these collisions. These clusters are ancient spherical structures that can contain hundreds of thousands of stars, all of which formed together, shortly after the Big Bang.

Within one of these clusters, stars average about a light year apart, and at their core, they can get as close to one another as the radius of our Solar System. With all these stars buzzing around for billions of years, you can imagine they’ve gotten up to some serious mischief.

Within globular clusters there are these mysterious blue straggler stars. They’re large hot stars, and if they had formed with the rest of the cluster, they would have detonated as supernovae billions of years ago. So scientists figure that they must have formed recently.

How? Astronomers think they’re the result of a stellar collision. Perhaps a binary pair of stars merged, or maybe two stars smashed into one another.

Professor Mark Morris of the University of California at Los Angeles in the Department of Physics and Astronomy helps to explain this idea.

“When you see two stars colliding with each other, it depends on how fast they’re moving. If they’re moving at speeds like we see at the center of our galaxy, then the collision is extremely violent. If it’s a head-on collision, the stars get completely splashed to the far corners of the galaxy. If they’re merging at slower velocities than we see at our neck of the woods in our galaxy, then stars are more happy to merge with us and coalesce into one single, more massive object.”

There’s another place in the Milky Way where you’ve got a dense collection of stars, racing around at breakneck speeds… near the supermassive black hole at the center of the galaxy.

This monster black hole contains the mass of 4 million times the Sun, and dominates the region around the center of the Milky Way.

This artist's concept illustrates a supermassive black hole with millions to billions times the mass of our sun. Supermassive black holes are enormously dense objects buried at the hearts of galaxies. Image credit: NASA/JPL-Caltech
Supermassive black holes are enormously dense objects buried at the hearts of galaxies. Image credit: NASA/JPL-Caltech

“The core of the Milky Way is one of those places where you find the extremes of nature. The density of stars there is higher than anywhere else in the galaxy,”Professor Morris continues. “Overall, in the center of our galaxy on scales of hundreds of light years, there is much more gas present than anywhere else in the galaxy. The magnetic field is stronger there than anywhere else in the galaxy, and it has it’s own geometry there. So it’s an unusual place, an energetic place, a violent place, because everything else is moving so much faster there than you see elsewhere.”

“We study the stars in the immediate vicinity of the black hole, and we find that there’s not as many stars as one might have expected, and one of the explanations for that is that stars collide with each other and either eliminate one another or merge, and two stars become one, and both of those processes are probably occurring.”

Stars whip around it, like comets dart around our Sun, and interactions are commonplace.

There’s another scenario that can crash stars together.

The Milky Way mostly has multiple star systems. Several stars can be orbiting a common center of gravity. Many are great distances, but some can have orbits tighter than the planets around our Sun.

When one star reaches the end of its life, expanding into a red giant, It can consume its binary partner. The consumed star then strips away 90% of the mass of the red giant, leaving behind a rapidly pulsating remnant.

What about when galaxies collide? That sounds like a recipe for mayhem.
Surprisingly, not so much.

“That’s actually a very interesting question, because if you imagine two galaxies colliding, you’d imagine that to be an exceptionally violent event,’ Professor Morris explains. “But in fact, the stars in those two galaxies are relatively unaffected. The number of stars that will collide when two galaxies collide is possibly counted on the fingers of one or two hands. Stars are so few and far between that they just aren’t going to meet each other with any significance in a field like that.”

Galaxy mergers, such as the Mice Galaxies will be part of Galaxy Zoo's newest project.  Credit: Hubble Space Telescope
The Mice galaxies merging. Credit: Hubble Space Telescope

“What you see when you see two galaxies collide, however, on the large scale, is that the tidal forces of the two galaxies will rip each of the galaxies apart in terms of what it will look like. Streams of stars will be strewn out in various directions depending on the precise history of the interaction between the two galaxies. And so, eventually over time, the galaxies will merge, the whole configuration of stars will settle down into something that looks unlike either of the two initially colliding galaxies. Perhaps something more spheroidal or spherical, and it might look more like an elliptical galaxy than the spiral galaxy that these two galaxies now are.”

Currently, we’re on a collision course with the Andromeda Galaxy, and it’s expected we’ll smash into it in about 4 billion years. The gas and dust will collide and pile up, igniting an era of furious star formation. But the stars themselves? They’ll barely notice. The stars in the two galaxies will just streak past each other, like a swarm of angry bees.

Phew.

So, good news! When you’re imagining a worse day, you won’t have to worry about our Sun colliding with another star. We’re going to be safe and sound for billions of years. But if you live in a globular cluster or near the center of the galaxy, you might want to check out some property here in the burbs.

Thanks to Professor Mark Morris at UCLA – visit their Physics and Astronomy program homepage here.

What is the Milky Way?

Artist's conception of the Milky Way galaxy. Credit: Nick Risinger
Artist's conception of the Milky Way galaxy. Credit: Nick Risinger

When you look up at the night sky, assuming conditions are just right, you might just catch a glimpse of a faint, white band reaching across the heavens. This band, upon closer observation, looks speckled and dusty, filled with a million tiny points of light and halos of glowing matter. What you are seeing is the Milky Way, something that astronomers and stargazers alike have been staring up at since the beginning of time.

But just what is the Milky Way? Well, simply put, it is the name of the barred spiral galaxy in which our solar system is located. The Earth orbits the Sun in the Solar System, and the Solar System is embedded within this vast galaxy of stars. It is just one of hundreds of billions of galaxies in the Universe, and ours is called the Milky Way because the disk of the galaxy appears to be spanning the night sky like a hazy band of glowing white light. Continue reading “What is the Milky Way?”

Astronomers Refine Distances to our Closest Spiral-Galaxy Neighbors

M31 and M33 are two of the nearest spiral galaxies, and can form the basis for determining distances to more remote spiral galaxies and constraining the expansion rate of the Universe (the Hubble constant).  Hence the relevance and importance of several new studies that employed near-infrared data to establish solid distances for M31 (Andromeda) and M33 (Triangulum) (e.g., Gieren et al. 2013), and aimed to reduce existing uncertainties tied to the fundamental parameters for those galaxies.  Indeed, reliable distances for M31 and M33 are particularly important in light of the new Hubble constant estimate from the Planck satellite, which is offset relative to certain other results, and that difference hinders efforts to ascertain the nature of dark energy (the mysterious force theorized as causing the Universe’s accelerated expansion).

Gieren et al. remarked that, “a number of new distance determinations to M33 … span a surprisingly large interval … which is a cause of serious concern. As the second-nearest spiral galaxy, an accurate determination of [M33’s] distance is a crucial step in the process of building the cosmic distance ladder.”  Concerning M31, Riess et al. 2012 likewise remarked that “M31, the nearest analogue of the Milky Way Galaxy, has long provided important clues to understanding the scale of the Universe.

 The new Gieren and Riess et al. distances are based on near-infrared observations, which are pertinent because radiation from that part of the electromagnetic spectrum is less sensitive than optical data to absorption by dust located along our sight-line (see the figure below).  Properly accounting for the impact of dust is a principal problem in cosmic distance scale work, since it causes targets to appear dimmer.  “different assumptions about [dust obscuration] are a prime source for the discrepancies among the various distance determinations for M33.” noted Gieren et al., and the same is true for the distance to M31 (see Riess et al.).

Optical and near-infrared images highlight how dust obscures light emitted from a target along the line-of-sight.  The near-infrared observations are less sensitive to that obscuration (image credit: Alves et al. 2001).
Optical and near-infrared images highlight how dust obscures light emitted from targets along the sight-line, and that the level of obscuration is wavelength dependent. New distances established for M31 and M33 are based on near-infrared observations, which are less sensitive to that obscuration (image credit: Alves et al. 2001).

The Gieren and Riess et al. distances to M33 and M31, respectively, were inferred from observations of Cepheids.   Cepheids are a class of variable stars that exhibit periodic brightness variations (they pulsate radially).  Cepheids can be used as distance indicators because their pulsation period and mean luminosity are correlated.  That relationship was discovered by Henrietta Leavitt in the early 1900s.  A pseudo period-luminosity relation derived for M31 Cepheids is presented below.

Gieren et al. observed 26 Cepheids in M33 and established a distance of ~2,740,000 lightyears.  The team added that, “As the first modern near-infrared Cepheid study [of] M33 since … some 30 years … we consider this work as long overdue …”  Astronomers often cite distances to objects in lightyears, which defines the time required for light emitted from the source to reach the observer. Despite the (finite) speed of light being 300,000,000 m/s, the rays must traverse “astronomical” distances.   Gazing into space affords one the unique opportunity to peer back in time.

A relation exists between a Cepheid's a periodic brightness variations and its luminosity.  Astronomers use that relation, which was discovered in the early 1900s by Henrietta Leavitt, to establish distances to galaxies.  In the above figure the horizontal axis features the pulsation period, and the vertical axis a proxy  for luminosity (image credit: Fig 2 in Riess et al., 2013 arXiv/ApJ).
A relation exists between a Cepheid’s periodic brightness variations and its mean luminosity. Astronomers use that trend, which was discovered in the early 1900s by Henrietta Leavitt, to establish distances to galaxies hosting Cepheids. In the above figure the horizontal axis features the pulsation period, and the vertical axis defines a proxy for luminosity (image credit: Fig 2 from Riess et al., arXiv/ApJ).

The distances to M33 shown below convey seminal points in the evolution of humanity’s knowledge.  The scatter near the 1920s stems partly from a debate concerning whether the Milky Way and the Universe are synonymous.  In other words, do galaxies exist beyond the Milky Way?  The topic is immortalized in the famed great debate (1920) featuring H. Shapley and H. Curtis (the latter argued for an extragalactic scale).  The offset between the pre-1930 and post-1980 data result in part from a nearly two-fold increase in the cosmic distance scale recognized circa 1950 (see also Feast 2000).   Also evident is the scatter associated with the post-1980 distances, which merely reinforces the importance of the new high-precision distance estimates.

Riess et al. obtained data for some 70 Cepheids and determined a distance for M31 of ~2,450,000 lightyears.  The latter is corroborated by a new study by Contreras Ramos et al. 2013 (d~2,540,000 ly), whose distance estimate relied on data for stars in a M31 globular cluster.

A subset of the distances estimated for M33, as compiled from estimates featured in the NASA/IPAC Extragalactic Database (Steer & Madore). On the vertical axis is the distance to the galaxy in units of lightyears, and  the year is cited on the horizontal axis.  The red arrow and black datum indicate the new near-infrared based distance from Gieren et al. 2013 (image credit: DM).
A subset of the distances deduced for M33, as compiled from estimates featured in the NASA/IPAC Extragalactic Database (Steer & Madore). On the vertical axis is the distance to the galaxy in units of lightyears, and the year is cited on the horizontal axis.  The red arrow and black datum indicate the new near-infrared based distance from Gieren et al. (image credit: DM).

Top-class instruments and telescopes are needed to obtain reliable measurements of stars in galaxies nearly 3,000,000 million lightyears away.  Gieren et al. utilized the 8.2-m Very Large Telescope (Yepun) instrument shown below, while Riess and Contreras Ramos et al. analyzed observations from the Hubble Space Telescope.  Riess et al. acquired images of M31 via the new Wide-field Camera 3, which replaced the Wide-field and Planetary Camera 2 (“The Camera That Saved Hubble“) during the famed 2009 servicing mission.

The new results mark the culmination of a century’s worth of effort aimed at securing precise distances for our Galaxy’s local spiral kin (M31 and M33).  However, the offset between the Planck and certain Cepheid/SN-based determinations of the Hubble constant demands that research continue in order to identify uncertainties associated with the methods.

Gieren et al. used the 8.2-m Very Large Telescope (Yepun) to image M33, and deduce the distance to that galaxy (image credit: ESO).
Gieren et al. used the 8.2-m Very Large Telescope (Yepun) to image stars in M33, and deduce the distance to that galaxy (image credit: G. Hüdepohl/ESO).

The Gieren et al. findings have been accepted for publication in the Astrophysical Journal (ApJ), and a preprint is available on arXiv.   Both the Riess and Contreras Ramos et al. studies are likewise published in ApJ.  The interested reader desiring additional information on the cosmic distance scale and Cepheids will find the following resources pertinent: the AAVSO’s article on Delta Cephei (the namesake for the class of Cepheid variables), Freedman & Madore (2010)Tammann & Reindl 2012, Fernie 1969, the NASA/IPAC Extragalactic Database, G. Johnson’s Miss Leavitt’s Stars: The Untold Story of the Woman Who Discovered How to Measure the Universe, D. Fernie’s Setting Sail for the Universe: Astronomers and their Discoveries, Nick Allen’s The Cepheid Distance Scale: A History, D. Turner’s Classical Cepheids After 228 Years of Study, J. Percy’s Understanding Variable Stars.

Comet PANSTARRS Meets the Andromeda Galaxy — More Amazing Images

Comet PANSTARRS and M31 on April 4, 2013, as seen from Sweden. Credit and copyright: Göran Strand.

More of our readers had success in capturing the awesomeness of seeing Comet PANSTARRS encounter the Andromeda Galaxy (M31) in the night sky. Göran Strand sent us this absolutely gorgeous image, taken from 70 km north of Östersund, Sweden — a really dark site with no light pollution. “This photo is a 30 minute exposure through my 300mm/f2.8 lens using my full format Nikon D3s camera,” Göran said. “Besides seeing the comet and the galaxy, I also got to see 4 elks, 2 meteors, 1 bolide and 1 aurora. So all in all, it was a good night!”

That’s for sure!

See more images below of this great meet-up in the skies, and see our earlier post of our readers’ images here.

Comet C/2011 L4 Panstarrs and the Andromeda Galaxy: Two Frame Mosaic from New Mexico Skies, April 4, 2013. Taken from New Mexico Skies at 23:22  UT using an FSQ 10.6-cm and STL11K camera.  Credit and copyright: Joseph Brimacombe.
Comet C/2011 L4 Panstarrs and the Andromeda Galaxy: Two Frame Mosaic from New Mexico Skies, April 4, 2013.
Taken from New Mexico Skies at 23:22 UT using an FSQ 10.6-cm and STL11K camera. Credit and copyright: Joseph Brimacombe.
The encounter between Comet PANSTARRS and the Andromeda Galaxy, as seen from Ireland. 'A difficult image to capture due to low cloud, the low altitude of the target and tracking Issue.'  Image details: Date: 03 Apr 2013, 22:30-23:30 Exposure: 9 x 5min, ISO 1600, F5, 6 x dark frames, 6 x flats frames. Equipment: Canon 1000D, CG5 Mount, Sigma 70-300mm set at 200mm. Credit and copyright: Brendan Alexander.
The encounter between Comet PANSTARRS and the Andromeda Galaxy, as seen from Ireland. ‘A difficult image to capture due to low cloud, the low altitude of the target and tracking Issue.’ Image details: Date: 03 Apr 2013, 22:30-23:30
Exposure: 9 x 5min, ISO 1600, F5, 6 x dark frames, 6 x flats frames.
Equipment: Canon 1000D, CG5 Mount, Sigma 70-300mm set at 200mm. Credit and copyright: Brendan Alexander.
Comet PANSTARRS and M31 taken from the Scottish Dark Sky Observatory on April 3, 2013. Credit and copyright: Dave Hancox via Google+.
Comet PANSTARRS and M31 taken from the Scottish Dark Sky Observatory on April 3, 2013. Credit and copyright: Dave Hancox via Google+.
Comet C/2011 L4 (PANSTARRS) and M31 (Andromeda Galaxy) taken from just outside St Clears, Carmarthenshire, Wales on 29th March 2013 around 9pm. Credit and copyright: Pete Newman.
Comet C/2011 L4 (PANSTARRS) and M31 (Andromeda Galaxy) taken from just outside St Clears, Carmarthenshire, Wales on 29th March 2013 around 9pm. Credit and copyright: Pete Newman.

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Incredible Views: Comet PANSTARRS Meets the Andromeda Galaxy

Two objects 2.5 million lightyears apart... PanSTARRS & Andromeda. Credit and copyright: Brendan Alexander.

We warned you it was going to happen, and here’s visual proof! In this comet encounter of the extragalactic kind, Comet PanSTARRS and the Andromeda Galaxy met each other in the skies above Earth. This great image by Brendan Alexander in Ireland shows the spectacular view. He said it was “a difficult image to capture due to low cloud, the low altitude of the target and tracking issue. I hope to get the chance to improve on this!”

Here’s another image from UT reader Anna Morris:


Comet PANSTARRS and the Andromeda galaxy over Suffolk, England on April 2, 2013. This composite images shows the movement of the comet during the imaging session. Credit and copyright: Anna Morris.
Comet PANSTARRS and the Andromeda galaxy over Suffolk, England on April 2, 2013. This composite images shows the movement of the comet during the imaging session. Credit and copyright: Anna Morris.

Want to see this meetup for yourself? Tonight might be even better:

Comet PANSTARRS shown every three days as it moves across Andromeda, passing near the Andromeda Galaxy around April 3. You can use Cassiopeia to point you to Beta Andromedae and from there to the comet.  The map shows the sky facing northwest about one hour after sunset. Comet and galaxy brightness are exaggerated for the sake of illustration. Stellarium
Comet PANSTARRS shown every three days as it moves across Andromeda, passing near the Andromeda Galaxy around April 3. You can use Cassiopeia to point you to Beta Andromedae and from there to the comet. The map shows the sky facing northwest about one hour after sunset. Comet and galaxy brightness are exaggerated for the sake of illustration. Stellarium

Did you capture this event, too? Let us know, or upload your images to our Flickr page.

Weekly SkyWatcher’s Forecast: October 29 – November 4, 2012

The Andromeda Galaxy Courtesy of Bob Kocar

Greetings, fellow SkyWatchers! Are you ready for some spooky targets this week? Then follow along as we take a look at the “Little Eyes”, the “Skull Nebula” and a star that’s as red as a drop of blood! If the weather permits, we’ll also be enjoying the Taruid Meteor Shower! Time to dust off those optics and meet me in the backyard…

Monday, October 29 – October’s Full Moon is known as the “Hunter’s Moon” or the “Blood Moon,” its name came from a time when hunters would stalk the fields by Luna’s cold light in search of prey before the winter season began. Pick a place at sunset to watch it rise – a place having a stationary point with which you can gauge its progress. Make note of the time when the first rim appears and then watch how quickly it gains altitude! How long does it take before it rises above your marker?

On this night in 1749, the French astronomer Le Gentil was at the eyepiece of an 18? focal length telescope. His object of choice was the Andromeda Galaxy, which he believed to be a nebula. Little did he know at the time that his descriptive notes also included M32, a satellite galaxy of M31. It was the first small galaxy discovered, and it would be another 175 years before these were recognized as such by Edwin Hubble.

Even though it’s very bright tonight, take the time to view the Andromeda Galaxy for yourself. Located just about a degree west of Nu Andromeda, this ghost set against the starry night was known as far back as 905 AD, and was referred to as the “Little Cloud.” Located about 2.2 million light-years from our solar system, this expansive member of our Local Galaxy Group has delighted observers of all ages throughout the years. No matter if you view with just your eyes, a pair of binoculars or a large telescope, M31 still remains one of the most spectacular galaxies in the night.

Tuesday, October 30 – Tonight let’s have a look at the big, fat Moon as we return again with binoculars to identify the maria once again. Take the time to repeat the names to yourself and to study a map. One of the keys to successfully learning to identify craters is by starting with large, easily recognized features. Even though the Moon is very bright when full, try using colored or Moon filters with your telescope to have a look at the many surface features which throw amazing patterns across its surface. If you have none, a pair of sunglasses will suffice.

Look for things you might not ordinarily notice – such as the huge streak which emanates from crater Menelaus. Look at the pattern projected from Proclus – or the intense little dot of little-known Pytheas north of Copernicus. It’s hard to miss the blinding beacon of Aristarchus! Check the southeastern limb where the edge of Furnerius lights up the landscape…or how a nothing crater like Censorinus shines on the southeast shore of Tranquillitatis, while Dionysus echoes it on the southwest. Could you believe Manlius just north of central could be such a perfect ring – or that Anaxagoras would look like a northern polar cap? On the eastern limb we see the bright splash ray patterns surrounding ancient Furnerius – yet the rays themselves emanate from the much younger crater Furnerius A. All over the visible side, we see small points light up: a testament to the Moon’s violent past written in its scarred lines. Take a look now at the western limb…for the sunrise is about to advance around it.

Wednesday, October 31 – Happy Halloween! Many cultures around the world celebrate this day with a custom known as “Trick or Treat.” Tonight instead of tricking your little ghouls and goblins, why not treat them to a sweet view through your telescope or binoculars? What Halloween would be complete without a witch?! Easily found from a modestly dark site with the unaided eye, the Pleiades can be spotted well above the northeastern horizon within a couple of hours of nightfall. To average skies, many of the 7 bright components will resolve easily without the use of optical aid, but to telescopes and binoculars? M45 (Right Ascension: 03 : 47.0 – Declination: +24 : 07) is stunning…

First let’s explore a bit of history. The recognition of the Pleiades dates back to antiquity and its stars are known by many names in many cultures. The Greeks and Romans referred to them as the “Starry Seven,” the “Net of Stars,” “The Seven Virgins,” “The Daughters of Pleione,” and even “The Children of Atlas.” The Egyptians referred to them as “The Stars of Athyr,” the Germans as “Siebengestiren” (the Seven Stars), the Russians as “Baba” after Baba Yaga, the witch who flew through the skies on her fiery broom. The Japanese call them “Subaru,” Norsemen saw them as packs of dogs and the Tonganese as “Matarii” (the Little Eyes). American Indians viewed the Pleiades as seven maidens placed high upon a tower to protect them from the claws of giant bears, and even Tolkien immortalized the stargroup in “The Hobbit” as “Remmirath.” The Pleiades have even been mentioned in the Bible! So, you see, no matter where we look in our “starry” history, this cluster of seven bright stars has been part of it. But, let’s have some Halloween fun!

The date of the Pleiades culmination (its highest point in the sky) has been celebrated through its rich history by being marked with various festivals and ancient rites – but there is one particular rite that really fits this occasion! What could be more spooky on this date than to imagine a group of Druids celebrating the Pleiades’ midnight “high” with Black Sabbath? This night of “unholy revelry” is still observed in the modern world as “All Hallow’s Eve” or more commonly as Halloween. Although the actual date of the Pleiades midnight culmination is now on November 21 instead of October 31, why break with tradition? Thanks to its nebulous regions, M45 looks wonderfully like a “ghost” haunting the starry skies.

Treat yourself and your loved ones to the “scariest” object in the night. Binoculars give an incredible view of the entire region, revealing far more stars than are visible with the naked eye. Small telescopes at lowest power will enjoy M45?s rich, icy-blue stars and fog-like nebulosity. Larger telescopes and higher power reveal many pairs of double stars buried within its silver folds. No matter what you choose, the Pleiades definitely rock!

Thursday, November 1 – On this day in 1977, Charles Kowal made a wild discovery – Chiron. This represented the first discovery of a multitude of tiny, icy bodies that lie in the outer reaches of our solar system. Collectively known as Centaurs, they reside in unstable orbits between Jupiter and Neptune and are almost certainly “refugees”” from the Kuiper Belt.

Tonight let’s go for something small, but white-hot as we head for a dwarf star and planetary nebula, NGC 246. You’ll find it just a bit more than a fistwidth north-northeast of Beta Ceti (RA 00 47 03.34 Dec -11 52 18.9).

First discovered by Sir William Herschel and cataloged as object V.25, this 8th magnitude planetary nebula has a wonderful patchy, diffuse structure that envelops four stars. Around 1600 light-years away, the nebulosity you can see around the exterior edges was once the outer atmosphere of a star much like our own Sun. At the center of the nebula lies the responsible star – the fainter member of a binary system. While it is now in the process of becoming a white dwarf, we can still enjoy the product of this expanding shell of gas that is often called the “Skull Nebula.”

Friday, November 2 – Celestial scenery alert! If you’re up when the Moon rises, be sure to look for the close pairing of Jupiter and the Moon – they’re only about a fingerwidth apart! For a few viewers in the southernmost Africa region, this is an occultation event, so be sure to check resources for websites like IOTA which will give you times for locations in your area. What a great photographic opportunity… Clear skies!
Today celebrates the birth of an astronomy legend – Harlow Shapely. Born in 1885, the American-born Shapley paved the way in determining distances to stars, clusters, and the center of our Milky Way galaxy. Among his many achievements, Shapely was also the Harvard College Observatory director for many years. Today in 1917 also represents the night first light was seen through the Mt. Wilson 100? telescope.

Of course, Dr. Shapley spent his fair share of time on the Hooker telescope as well. One of his many points of study was globular clusters, their distance, and their relationship to the halo structure of our galaxy. Tonight let’s have a look at a very unusual little globular located about a fistwidth south-southeast of Beta Ceti and just a couple of degrees north-northwest of Alpha Sculptor (RA 00:52:47.5 Dec -26:35:24), as we have a look at NGC 288.

Discovered by William Herschel on October 27, 1785, and cataloged by him as H VI.20, the class X globular cluster blew apart scientific thinking in the late 1980?s as a study of perimeter globulars showed it to be more than 3 million years older than similar globulars – thanks to the color magnitude diagrams of Hertzsprung and Russell. By identifying both its blue and red branches, it was shown that many of NGC 288?s stars are being stripped away by tidal forces and contributing to the formation of the Milky Way’s halo structure. In 1997, three additional variable stars were discovered in this cluster.
At magnitude 8, this small globular is easy for southern observers, but faint for northern ones. If you are using binoculars, be sure to look for the equally bright spiral galaxy NGC 253 to the globular’s north.

Saturday, November 3 – On this day in 1955, one of the few documented cases of a person being hit by a meteorite occurred. What are the odds on that? In 1957 the Russian space program launched its first “live” astronaut into space – Laika. Carried on board Sputnik 2, our canine hero was the first living creature to reach orbit. The speedily developed Sputnik 2 was designed with sensors to transmit the ambient pressure, breathing patterns and heartbeat of its passenger, and also had a television camera on board to monitor its occupant. The craft also studied ultraviolet and x-ray radiation to further assess the impact of space flight upon live occupants. Unfortunately, the technology of the time offered no way to return Laika to Earth, so she perished in space. On April 14, 1958, Laika and Sputnik 2 returned to Earth in a fiery re-entry after 2,570 orbits.

Since we’ve got the scope out, let’s go have another look at that galaxy we spied last night!

Discovered by Caroline Herschel on September 23, 1783, NGC 253 (RA 00 47.6 Dec -25 17) is the brightest member of a concentration of galaxies known as the Sculptor Group, near to our own local group and the brightest of all outside it. Cataloged as both H V.1 and Bennett 4, this 7th magnitude beauty is also known as Caldwell 65, and due to both its brightness and oblique angle is often called the “Silver Dollar Galaxy.” As part of the SAC 110 best NGCs, you can even spot this one if you don’t live in the Southern Hemisphere. At around 10 million light-years away, this very dusty, star-forming Seyfert galaxy rocks in even a modest telescope!

Sunday, November 4 – This morning will be the peak of the Southern Taurid meteor shower. Already making headlines around the world for producing fireballs, the Taurids will be best visible in the early morning hours, but the Moon will interfere. The radiant for this shower is, of course, the constellation of Taurus and red giant Aldeberan, but did you know the Taurids are divided into two streams?

It is surmised that the original parent comet shattered as it passed our Sun around 20,000 to 30,000 years ago. The larger “chunk” continued orbiting and is known as periodic comet Encke. The remaining debris field turned into smaller asteroids, meteors and larger fragments that often pass through our atmosphere creating the astounding “fireballs” known as bolides. Although the fall rate for this particular shower is rather low at 7 per hour, these slow traveling meteors (27 km or 17 miles per second) are usually very bright and appear to almost “trundle” across the sky. With the chances high all week of seeing a bolide, this makes a bit of quiet contemplation under the stars worthy of a morning walk. Be sure to look at how close Saturn is to the Moon!

For unaided eye or binocular observers – or those who just wish something a bit “different” tonight – have a look at 19 Pisces. You’ll find it as the easternmost star in the small “circlet” just south of the Great Square of Pegasus.

Also known as TX, you’ll find this one quite delightful for its strong red color. TX is a cool giant star which varies slightly in magnitude on an irregular basis. This carbon star is located anywhere from 400 to 1000 light-years away and rivals even R Leporis’ crimson beauty.

Until next week? Wishing you clear skies!

It’s Inevitable: Milky Way, Andromeda Galaxy Heading for Collision

This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth's night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. (Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger)

Astronomers have known for years that our Milky Way and its closest neighbor, the Andromeda galaxy, (a.k.a M31) are being pulled together in a gravitational dance, but no one was sure whether the galaxies would collide head-on or glide past one another. Precise measurements from the Hubble Space Telescope have now confirmed that the two galaxies are indeed on a collision course, headed straight for a colossal cosmic collision.

No need to panic for the moment, as this is not going to happen for another four billion years. And while astronomers say it is likely the Sun will be flung into a different region of our galaxy, Earth and the solar system will probably just go along for the ride and are in no danger of being destroyed.

“In the ‘worst-case-scenario’ simulation, M31 slams into the Milky Way head-on and the stars are all scattered into different orbits,” said team member Gurtina Besla of Columbia University in New York, N.Y. “The stellar populations of both galaxies are jostled, and the Milky Way loses its flattened pancake shape with most of the stars on nearly circular orbits. The galaxies’ cores merge, and the stars settle into randomized orbits to create an elliptical-shaped galaxy.”

The simulations Besla was talking about came from precise measurements by Hubble, painstakingly determining the motion of Andromeda, looking particularly at the sideways motion of M31, which until now has not been able to be done.

“This was accomplished by repeatedly observing select regions of the galaxy over a five- to seven-year period,” said Jay Anderson of STScI.

Right now, M31 is 2.5 million light-years away, but it is inexorably falling toward the Milky Way under the mutual pull of gravity between the two galaxies and the invisible dark matter that surrounds them both.

Of course, the collision is not like a head-on between two cars that takes place in an instant. Hubble data show that it will take an additional two billion years after the encounter for the interacting galaxies to completely merge under the tug of gravity and reshape into a single elliptical galaxy similar to the kind commonly seen in the local universe.

Astronomers said the stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today.

There’s also the complication of M31’s small companion, the Triangulum galaxy, M33. This galaxy will join in the collision and perhaps later merge with the M31/Milky Way pair. There is a small chance that M33 will hit the Milky Way first.

The astronomers working on this project said that they were able to make the precise measurements because of the upgraded cameras on Hubble, installed during the final servicing mission. This gave astronomers a long enough time baseline to make the critical measurements needed to nail down M31’s motion.

The Hubble observations and the consequences of the merger are reported in three papers that will appear in an upcoming issue of the Astrophysical Journal.

This series of photo illustrations shows the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy. Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas, and A. Mellinger

First Row, Left: Present day.
First Row, Right: In 2 billion years the disk of the approaching Andromeda galaxy is noticeably larger.
Second Row, Left: In 3.75 billion years Andromeda fills the field of view.
Second Row, Right: In 3.85 billion years the sky is ablaze with new star formation.
Third Row, Left: In 3.9 billion years, star formation continues.
Third Row, Right: In 4 billion years Andromeda is tidally stretched and the Milky Way becomes warped.
Fourth Row, Left: In 5.1 billion years the cores of the Milky Way and Andromeda appear as a pair of bright lobes.
Fourth Row, Right: In 7 billion years the merged galaxies form a huge elliptical galaxy, its bright core dominating the nighttime sky.

Source: HubbleSite See more images and videos here and here.

Andromeda Dwarf Galaxies Help Unravel The Mysteries Of Dark Matter

The circled cluster of stars is the dwarf galaxy Andromeda 29, which University of Michigan astronomers have discovered. The bright star within the circle is a foreground star within our own Milky Way galaxy. This image was obtained with the Gemini Multi-Object Spectrograph at the Gemini North telescope in Hawaii. Credit: Gemini Observstory/AURA/Eric Bell

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Yep. It’s that time of year again. Time to enjoy the Andromeda Galaxy at almost every observing opportunity. But now, rather than just look at the nearest spiral to the Milky Way and sneaking a peak at satellites M32 and M110, we can think about something more when we peer M31’s way. There are two newly discovered dwarf galaxies that appear to be companions of Andromeda!

Eric Bell, an associate professor in astronomy, and Colin Slater, an astronomy Ph.D. student, found Andromeda 28 and Andromeda 29 by utilizing the Sloan Digital Sky Survey and a recently developed star counting technique. To back up their observations, the team employed data from the Gemini North Telescope in Hawaii. Located at 1.1 million and 600,000 light-years respectively, Andromeda XXVIII and Andromeda XXIX have the distinction of being the two furthest satellite galaxies ever detected away from the host – M31. Can they be spotted with amateur equipment? Not hardly. This pair comes in about 100,000 fainter than Andromeda itself and can barely be discerned with some of the world’s largest telescopes. They’re so faint, they haven’t even been classified yet.

“With presently available imaging we are unable to determine whether there is ongoing or recent star formation, which prevents us from classifying it as a dwarf spheroidal or a dwarf irregular.” explains Bell.

The dwarf galaxy Andromeda 29, which University of Michigan astronomers have discovered, is clustered toward the middle of this image, obtained with the Gemini North telescope in Hawaii. Credit: Gemini Observstory/AURA/Eric Bell

In their work – published in a recent edition of the edition of the Astrophysical Journal Letters – the team of Bell and Slater explains how they were searching for dwarf galaxies around Andromeda to help them understand how physical matter relates to theoretical dark matter. While we can’t see it, hear it, touch it or smell it, we know it’s there because of its gravitational influence. And when it comes to gravity, many astronomers are convinced that dark matter plays a role in organizing galaxy structure.

“These faint, dwarf, relatively nearby galaxies are a real battleground in trying to understand how dark matter acts at small scales,” Bell said. “The stakes are high.”

Right now, current consensus has all galaxies embedded in surrounding dark matter… and each “bed” of dark matter should have a galaxy. Considering the volume of the Universe, these predictions are pretty much spot on – if we take only large galaxies into account.

“But it seems to break down when we get to smaller galaxies,” Slater said. “The models predict far more dark matter halos than we observe galaxies. We don’t know if it’s because we’re not seeing all of the galaxies or because our predictions are wrong.”

“The exciting answer,” Bell said, “would be that there just aren’t that many dark matter halos.” Bell said. “This is part of the grand effort to test that paradigm.”

Right or wrong… pondering dark matter and dwarf galaxies while observing Andromeda will add a whole new dimension to your observations!

For Further Reading: Andromeda XXVIII: A Dwarf Galaxy more than 350 kpc from Andromeda and Andromeda XXIX: A New Dwarf Spheroidal Galaxy 200 kpc from Andromeda.