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  • richardmitnick 1:53 pm on December 16, 2018 Permalink | Reply
    Tags: , , , , , , , Virgo supercluster   

    From EarthSky: “What is the Local Group?” 

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    From EarthSky

    How many galaxies are now known to lie within our Local Group of galaxies? How does our Milky Way rank, size-wise? And what about the vast superclusters beyond?

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    One view of the Local Group- a bit to constricted.The 3 largest galaxies in the Local Group are, in descending order, Messier 31 the Andromeda galaxy, the Milky Way, and Messier 33 also known as the Triangulum Galaxy

    Iconic view of the Local Group. Andrew Z. Colvin 3 March 2011

    We know where our galaxy is located, but only locally speaking. The Milky Way galaxy is one of more than 54 galaxies known as the Local Group. The three largest members of the group are our Milky Way (second-biggest), the Andromeda galaxy (biggest) and the Triangulum Galaxy. The other galaxies in the Local Group are dwarf galaxies, and they’re mostly clustered around the three larger galaxies.

    The Local Group does have a gravitational center. It’s somewhere between the Milky Way and the Andromeda Galaxy.

    The Local Group has a diameter of about 10 million light-years.

    Astronomers have also discovered that our Local Group is on the outskirts of a giant supercluster of galaxies, known as the Virgo Supercluster.

    Virgo Supercluster NASA

    Virgo Supercluster, NASA, Wikipedia

    At least 100 galaxy groups and clusters are located within the Virgo Supercluster. Its diameter is thought to be about 110 million light-years.

    The Virgo Supercluster may be part of an even-larger structure that astronomers call the Laniakea Supercluster.

    Laniakea supercluster. From Nature The Laniakea supercluster of galaxies R. Brent Tully, Hélène Courtois, Yehuda Hoffman & Daniel Pomarède at http://www.nature.com/nature/journal/v513/n7516/full/nature13674.html. Milky Way is the red dot.

    It consists of perhaps 100,000 galaxies stretched out over some 520 million light-years.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.orgin 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.

     
  • richardmitnick 10:25 am on December 11, 2017 Permalink | Reply
    Tags: Astronomers chart galaxy orbits in our Local Supercluster, , , , , , , Virgo supercluster   

    From EarthSky: “Astronomers chart galaxy orbits in our Local Supercluster” 

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    EarthSky

    December 10, 2017
    Deborah Byrd

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    In the [interactive in the full article, image above], you’ll notice the galaxies are moving toward something, a gravitational attractor represented by the big red dot more or less in the center of the mapped area (and in purple in the still graphic just above). This attractor is the Virgo Cluster, a large cluster of galaxies at the heart of the Virgo Supercluster (all located in the direction to the constellation Virgo in our sky; hence their names).

    Our home Milky Way galaxy (MW, yellow) and our companion Andromeda galaxy (M31, red) are participating in a downward flow away from a vast underdense region called the Local Void and toward the Virgo Cluster, represented by the large purple dot in this image. Most galaxies between us and the Virgo Cluster will eventually fall into the cluster but we lie slightly beyond the capture zone. Image via R. Brent Tully/ Institute for Astronomy, U Hawaii.

    “For the first time, we are not only visualizing the detailed structure of our Local Supercluster of galaxies, but we are also seeing how the structure developed over the history of the universe.”

    Look at the [above] graphic, for the yellow letters marked MW. Our Milky Way is part of what’s called the Local Group, which spans about 10 million light-years and contains several dozen galaxies. The Local Group, in turn, is part of the Virgo Supercluster, which spans just over 100 million light-years and is thought to contain at least 100 galaxy groups and clusters. [The work] is part of a study by a team of astronomers from Maryland, Hawaii, Israel, and France. They say it’s the most detailed map ever of the orbits of galaxies in our extended local neighborhood. It shows the past motions of some 1,400 galaxies within 100 million light-years of our Milky Way.

    Local Group. Andrew Z. Colvin 3 March 2011

    Virgo Supercluster, Wikipedia

    The Virgo Cluster alone – which is about 50 million light-years from us, or in the midst of the Virgo Supercluster’s 100 million light-years – has 600 trillion times the mass of our sun. These astronomers explained in their statement that the Virgo Cluster is pulling other galaxies toward itself, and absorbing them:

    Over a thousand galaxies have already fallen into the Virgo Cluster, while in the future all galaxies that are currently within 40 million light-years of the cluster will be captured. Our Milky Way galaxy lies just outside this capture zone. However the Milky Way and Andromeda galaxies, each with 2 trillion times the mass of the sun, are destined to collide and merge [with each other] in 5 billion years.

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

    The study [The Astrophysical Journal] [is] based on the measurement of 18,000 galaxy distances. The astronomers’ statement explained the interactive this way:

    “With the interactive model [in the full aticle], a viewer can pan, zoom, rotate, and pause/activate the time evolution of movement along orbits. The orbits are shown in a reference frame that removes the overall expansion of the universe.”

    The lead author of this study is Ed Shaya of the University of Maryland in collaboration with Brent Tully of University of Hawaii, Yehuda Hoffman of Hebrew University in Israel, and Daniel Pomarede of University of Paris-Saclay in France. These scientists used what they said is a novel method for determining galaxy orbits, which they called numerical action. Brent Tully said:

    “For the first time, we are not only visualizing the detailed structure of our Local Supercluster of galaxies but we are seeing how the structure developed over the history of the universe. An analogy is the study of the current geography of the Earth from the movement of plate tectonics.”

    The astronomers’ statement also explained:

    “These dramatic merger events are only part of a larger show. There are two overarching flow patterns within this volume of the universe. All galaxies in one hemisphere of the region – including our own Milky Way – are streaming toward a single flat sheet. In addition, essentially every galaxy over the whole volume is flowing, as a leaf would in a river, toward gravitational attractors at far greater distances …”

    Representations of the orbits in the Virgo Supercluster can also be seen in the video [in the full article]:

    Bottom line: A team of astronomers has made the most detailed map ever of the orbits of galaxies in our local supercluster. It shows the past motions of some 1,400 galaxies within 100 million light-years of our Milky Way.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.

     
  • richardmitnick 9:14 am on June 14, 2017 Permalink | Reply
    Tags: , , , , , Messier 89, Virgo supercluster   

    From Manu: “Messier 89, elliptical galaxy with outer shells and feathers” 


    Manu Garcia, a friend from IAC.

    The universe around us.
    Astronomy, everything you wanted to know about our local universe and never dared to ask.

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    Messier 89, elliptical galaxy with outer shells and feathers.

    This famous Messier object is a seemingly simple elliptical galaxy, surrounded by weak shells and plumes. The cause of the shells is currently unknown, but possibly tidal tails related to the remnants of the absorption of many small galaxies in the last billion years. Alternatively, shells can be like ripples in a pond, where a recent collision with another large galaxy created waves of density that ripple through this galactic giant. Regardless of the real cause, the featured image highlights the growing consensus that at least some elliptical galaxies have formed in the recent past and that the outer halos of most large galaxies are not really smooth but have complexities induced by frequent interactions And Acreciones of smaller nearby galaxies. The Halo of our own milky way galaxy is an example of such unexpected complexity. Messier 89 is a member of the nearby Virgo cluster of galaxies that is about 50 million light-years away.

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    Virgo Supercluster, Wikipedia

    Image Credit and copyright: Mark Hanson

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 2:17 pm on October 18, 2016 Permalink | Reply
    Tags: , , , Doppler effect, M98 (or NGC 4192), , Virgo supercluster   

    From Slate: “A Spiral Galaxy Defying the Cosmic Flow” 

    SLATE

    slate.com

    Oct. 18 2016
    Phil Plait

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    M98, a galaxy that, for a short time, is swimming upstream against the expansion of the Universe. ESO/Acknowledgements: Flickr user jbarring

    I’d like to introduce you to an interesting galaxy today. The reason it’s interesting is because it’s surprising, and in a way that caught me off guard.

    It’s called M98 (or NGC 4192; every object in the sky is in multiple catalogs and has multiple handles), and it’s a spiral galaxy much like the Milky Way. It’s located about 50 million light-years away, which isn’t exactly close on a cosmic scale but isn’t all that far away either. If I had to make an analogy, it’s like it’s in the next town over.

    We see M98 at a pretty low angle, so it appears nearly edge-on to us; spiral galaxies are pretty flat, and can have wildly different appearances depending on our viewing angle. Still, the spiral pattern is obvious enough, and you can see bright blue regions where stars are being born; those trace the arms. There is also lots of patchy dust along the arms; molecules of silica and aluminum as well as complex carbon-based molecules that are more like soot than anything else.

    I like the central region of the galaxy; it’s bright but from this angle is cut in half by a dust lane, distorting the apparent shape of the usually elliptical hub.

    All in all, it’s quite lovely, and that shot by the New Technology Telescope [NTT] really shows it off.

    ESO/NTT at Cerro La Silla, Chile
    ESO/NTT ESO NTT Interior
    ESO/NTT at Cerro La Silla, Chile

    But in that way it’s like a zillion other spirals. So what makes this one special?

    Unlike nearly every single other galaxy in the Universe, this one isn’t moving away from us. It’s moving toward us.

    There’s no danger of a collision! At its speed of 150 km/sec, it would take a hundred billion years to get here, so don’t wait up. Also, it’s probably not heading directly at us, because it’s part of the Virgo Cluster, a grouping of about thousand galaxies bound by their own gravity.

    Virgo Supercluster
    Virgo Supercluster

    It’s the closest true cluster to us, and our own small Local Group of a couple dozen galaxies is like a small town near a bigger one. M98 is part of the Virgo Cluster, so it’s in orbit around the cluster center. We’re way outside the cluster, so it can’t hit us.

    Here’s the fun bit. The Universe, as you may know, is expanding. One way to think of it is that space itself is getting bigger, and as it does galaxies are swept along with it. Galaxies aren’t really moving away from each other, they’re just floating along with the local flow.


    Access mp4 video here .

    But in many ways it’s like they really are moving away. One way is that their light is redshifted; the wavelength of the light they emit is stretched (it’s very similar to the Doppler effect that makes a motorcycle go EEEEEEeoowwwwwww as it passes you, changing the pitch of the noise). Practically every galaxy in the Universe shows this redshift, and in fact that’s how all this was discovered in the first place. The farther away a galaxy is, the more it’s light is shifted.

    But not every galaxy shows it. Close by galaxies have much lower redshifts, and if the galaxy itself is moving rapidly through space (and not just with it), that local velocity will get added to or subtracted from the recession velocity.

    One example of this is the monstrous Andromeda galaxy, which is headed toward us at high speed.

    Andromeda Galaxy Adam Evans
    Andromeda Galaxy Adam Evans

    We actually will collide with it, though not for quite some time (like, 4 billion years). But it shows a distinct blueshift in its light; it’s moving around faster than space is expanding.

    M98 is doing the same thing. That surprised me when I saw it in a catalog; it’s far enough away that the Universal expansion should make it recede from us at about 1,000 km/sec.

    But then I saw it was in the Virgo Cluster, and I understood. The massive gravity of all those galaxies means they orbit the center at a decent clip, so some galaxies are redshifted more than average as they head away from us, in the part of their orbit taking them to the other side of the cluster. Some have lower velocities because they’re headed toward us in their orbits.

    But M98 is still unusual because it can completely overcome the recession of the cluster, and actually be physically headed toward us. That’s almost certainly because it’s recently interacted with another galaxy in the cluster; when galaxies pass each other one can be flung away at high speed, something like a slingshot effect. M98 may very well have done this, and that’s why it’s blueshifted, not redshifted.

    As you look to more distant clusters this gets rare or nonexistent, because at that distance the cosmic expansion dominates, and it doesn’t matter how fast the galaxy is moving: It can’t overcome that recession. All galaxies past a certain distance are redshifted, which is yet another reason (among many, many others) that we know the Universe actually is expanding.

    That’s pretty cool. I like surprises when I’m reading up on lovely astronomical objects; that means I’ve learned something. M98 is headed toward us, a rare blueshifted galaxy. Huh. That just adds to its beauty and intrigue to me.

    It’s a really beautiful Universe, and it’s also a really interesting one. I’d say that’s its best quality.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Slate is a daily magazine on the Web. Founded in 1996, we are a general-interest publication offering analysis and commentary about politics, news, business, technology, and culture. Slate’s strong editorial voice and witty take on current events have been recognized with numerous awards, including the National Magazine Award for General Excellence Online. The site, which is owned by Graham Holdings Company, does not charge for access and is supported by advertising revenues.

     
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