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  • richardmitnick 2:17 pm on October 18, 2016 Permalink | Reply
    Tags: , , , Doppler effect, M98 (or NGC 4192), Phil Plait at Slate,   

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

    SLATE

    slate.com

    Oct. 18 2016
    Phil Plait

    1
    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.

     
  • richardmitnick 12:40 pm on June 13, 2016 Permalink | Reply
    Tags: , , JAXA Akatsuki, Phil Plait at Slate,   

    From Phil Plait at Slate: “Akatsuki Reveals a Hot, Dynamic Venus” 

    SLATE

    slate.com

    June 13 2016
    Phil Plait

    1
    A highly unusual infrared view of Venus, taken by the Japanese Akatsuki probe. ISAS/JAXA

    That stunning image above really threw me for a moment. If I hadn’t seen the caption first, it seriously would’ve taken me a second or two to figure out what planet it must be.

    That’s Venus. Honestly, I’ve never seen an image of our sister planet that looks anything quite like that (well, maybe just a little; see below). Usually Venus just looks, well, white. In visible light, at least, the kind our eyes see. Sometimes you can see subtle features, but nothing like this.

    That shot was taken by the Japanese Akatsuki (“Dawn”) spacecraft, which entered Venus orbit in late 2015.

    JAXA AKATSUKI
    JAXA AKATSUKI

    This part is amazing: It was launched in March 2010 and arrived at Venus in December of that year, but due to a thruster misfiring it wound up not going into orbit around Venus initially. It orbited the Sun for five years, and incredibly engineers were able to insert it into Venus orbit using only its attitude control thrusters, very low thrust rockets used normally just to change the spacecraft’s angle to the planet. By doing so, they saved the mission.

    And now Akatsuki is returning science to Earth. The image above is a combination of two infrared shots at wavelengths of 1.735 microns (shown as red) and 2.26 microns (shown as blue); a pseudo-green frame was crated combining the two together. The color choice is a bit odd, since usually the longer wavelength image is shown as red. But who am I to argue with such a phenomenal image?

    The bright white crescent on the left is the day side of Venus, and the orange band is actually twilight; the ridiculously thick atmosphere of Venus (90 times the pressure of Earth’s atmosphere at ground level!) spreads out the sunlight, causing a wide band of scattered sunlight.*

    But it’s the structure of the clouds on the night side of the planet that’s so amazing. The two different wavelengths used are sensitive to different sized cloud particles in Venus’ atmosphere and really show the atmospheric structure.

    Venus is really odd: It rotates extremely slowly, taking 243 days to spin just once! The atmosphere, however, moves much more rapidly. At least, in the troposphere it does, up to a height of about 65 kilometers. It super-rotates, going around the planet faster than the planet spins. This effect is strongest at the equator, and decreases toward the poles. You can see that in the image; the sideways V-shape to the clouds reveals that.

    In fact, I mentioned that the IR image does look a little like another one of Venus I’ve seen, in this case what it looks like in the ultraviolet:

    3
    Venus in ultraviolet light. ISAS/JAXA

    That image was also taken by Akatsuki as it reached Venus orbit. You can also see the unusual pattern in the clouds there. Previous UV images have shown this as well.

    The folks at the Japanese space agency JAXA also released this fascinating short animation showing the cloud motion:

    4
    ISAS/JAXA

    That was taken in the infrared, four images taken four hours apart each. The motion you see is almost entirely due to the clouds super-rotating; Venus hardly spun at all during that time (the spacecraft was about 360,000 kilometers from the planet at the time, so its orbital velocity is low, and doesn’t contribute much to the motion seen either).

    Akatsuki is still warming (haha) to its task at Venus. One of the most interesting things I’m waiting for is lightning data. Yes, seriously! Akatsuki has a Lightning and Airglow Camera that hopefully will settle a decades-long debate over whether Venus has lightning or not. That camera will be returning data pretty soon, so that’ll be nice to see.

    Venus is such a fascinating place. Far hotter than Earth, an atmosphere that’s almost entirely carbon dioxide, tremendous surface pressure, a thick crust covered in volcanic features … it’s so close to being another Earth yet misses by a country kilometer. What happened? Why is it not Earth’s twin, but Earth’s evil twin? We’re still trying to figure that out, and Akatsuki will help tremendously.

    Update, June 13, 2016: Mark McCaughrean, senior space adviser for the European Space Agency, reminded me that the ESA Venus Express probe also took amazing images of Venus.

    ESA/Venus Express
    ESA/Venus Express

    To be honest, this simply slipped my mind! I’ve thought about this before; we’ve had so many missions to so many planets now that it can be hard to remember them all. What times we live in! I’ve written about Venus Express many times, and because why not, here’s NASA’s Magellan mission, too.

    5
    Magellan imaged more than 98% of Venus at a resolution of about 100 meters.

    Magellan mission to Venus spacecraft
    NASA/Magellan mission to Venus spacecraft

    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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