A Galaxy That Is Blueshifted Would Be Moving
A Spiral Galaxy Defying the Cosmic Flow
ESO/Acknowledgements: Flickr user jbarring
I'd like to introduce you lot to an interesting galaxy today. The reason information technology's interesting is because information technology's surprising, and in a mode that caught me off baby-sit.
It's called M98 (or NGC 4192; every object in the sky is in multiple catalogs and has multiple handles), and it'southward a spiral milky way much like the Milky Way. It's located about 50 1000000 light-years away, which isn't exactly close on a cosmic scale but isn't all that far away either. If I had to brand an analogy, it's like information technology'southward in the side by side town over.
Nosotros see M98 at a pretty low angle, and so it appears nearly edge-on to u.s.a.; screw galaxies are pretty flat, and tin can accept wildly unlike appearances depending on our viewing bending. Nevertheless, the spiral blueprint is obvious enough, and you lot tin run across bright blue regions where stars are being built-in; those trace the arms. There is too lots of patchy grit along the arms; molecules of silica and aluminum too every bit circuitous carbon-based molecules that are more like soot than anything else.
I like the fundamental region of the galaxy; it's bright but from this angle is cut in one-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 really shows it off.
But in that fashion it's like a zillion other spirals. And then what makes this one special?
Unlike nearly every single other galaxy in the Universe, this one isn't moving abroad from us. Information technology'southward 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 become hither, and then don't look upwards. Too, it's probably not heading directly at the states, because it'southward part of the Virgo Cluster, a grouping of virtually thousand galaxies bound by their own gravity. Information technology'southward the closest true cluster to us, and our own small Local Group of a couple dozen galaxies is like a small town almost a bigger 1. M98 is function of the Virgo Cluster, so information technology's in orbit around the cluster center. Nosotros're way outside the cluster, so information technology can't hit united states.
Hither's the fun bit. The Universe, equally you may know, is expanding. I style to think of it is that space itself is getting bigger, and equally information technology does galaxies are swept along with it. Galaxies aren't really moving abroad from each other, they're just floating along with the local flow.
But in many ways information technology's like they really are moving away. One way is that their light is redshifted; the wavelength of the low-cal they emit is stretched (it'due south very similar to the Doppler effect that makes a motorcycle get EEEEEEeoowwwwwww as it passes you lot, changing the pitch of the noise). Practically every milky way 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 than it'due south light is shifted.
But non every galaxy shows it. Close past galaxies take much lower redshifts, and if the galaxy itself is moving rapidly through space (and not but with it), that local velocity volition get added to or subtracted from the recession velocity.
One example of this is the monstrous Andromeda galaxy, which is headed toward us at loftier speed. We actually will collide with it, though non for quite some fourth dimension (like, 4 billion years). But it shows a distinct blueshift in its light; it'due south moving around faster than infinite is expanding.
M98 is doing the aforementioned thing. That surprised me when I saw it in a catalog; it'due south far enough away that the Universal expansion should make information technology recede from usa at about ane,000 km/sec.
But then I saw information technology 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 office of their orbit taking them to the other side of the cluster. Some have lower velocities because they're headed toward usa in their orbits.
But M98 is however unusual because information technology can completely overcome the recession of the cluster, and actually be physically headed toward us. That's most certainly because information technology's recently interacted with another galaxy in the cluster; when galaxies pass each other one can be flung away at loftier speed, something like a slingshot effect. M98 may very well have done this, and that's why it'southward blueshifted, not redshifted.
As yous look to more afar clusters this gets rare or nonexistent, because at that distance the catholic expansion dominates, and it doesn't matter how fast the galaxy is moving: It can't overcome that recession. All galaxies past a certain altitude are redshifted, which is yet another reason (among many, many others) that nosotros know the Universe actually is expanding.
That's pretty cool. I like surprises when I'm reading upward 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.
Information technology's a really cute Universe, and it'south too a actually interesting 1. I'd say that's its best quality.
Source: https://slate.com/technology/2016/10/m98-is-a-rare-blueshifted-galaxy.html
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