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Old 12-05-2016, 08:24 AM
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Weltevreden SA (Dana)
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One steak: ESO 92-SC05. One sizzle: VDBH 176. III

One steak, one sizzle, Part III

So where DOES our Galaxy get its gas?

This long tra-la-la started with the simple notion that in 2.6 billion years our Milky Way will run out of gas. We’re on our way to Virgo, but that’s two or three tankfuls away. So what if we DO run out of gas? What then? The Hitchhiker’s Guide to the Galaxy doesn’t list petrol sheds. If we look around, plenty of galaxies have emptied their tanks before us. We call them SO or lenticular galaxies. Lenticulars have the structural properties of spirals but the gas content of ellipticals. Which is to say, they are running on fumes.

The two oddball clusters ESO 92-SC05 and BH176 we have looked at here are odd only in that we are not certain exactly where they originated and how they got here. We can be perfectly content to simply enjoy the fun of locating and viewing them. Piffles to the eye though they be, they nonetheless thrill.

The great joy in astronomy is solving the improbable to see the impossible. From the above we can conclude that the Galactic ingestion of dwarf galaxies which gave us BH176 and ESO 092-SC05 could hardly fill our Galaxy’s gas tank. They—and all those other 15-odd stellar streams girding us from on high—only fill the Galactic halo with stars and the Galactic corona with gas. Heat yes, fire no. They do little to fill the disc with the raw materials to get us past the 2.6 Gyr “Empty” mark that would gum up the wheels of our voyage to Virgo. The energy transfer from dwarf into halo will in fact contribute to disc heating (1st Law of Thermodynamics), and warmer discs form more stars than cooler ones (2nd Law of Thermodynamics). If you are on the edge of your chair just panting to read the gritty details, start with §2.5 of this paper.

If we take a closer look at those wispy ellipses whirling all around us, they aren’t at the same radial distance. They aren’t streaming at the same velocity and in the same direction. They won’t all infall into the Galactic fuel tank at once. Each adds a few dribs and drabs, but not a full tank. They won’t contribute the one thing a spinning galaxy disc needs most: more spin. If our Galactic disc is to make more stars, it needs the gas’s angular energy as well as its nuclear energy. There’s only one source that can provide both: the eonic inflow of gas along cosmic filaments. They are the sigh across forever that powers our vastness.

Intergalactic petrol pumps fill from immense pipelines streaming along the far reaches of the cosmic web. The Big Bang shivered within from the shock of origin. The shivers introduced tiny quantum imperfections in the searing ball of matter blowing outward after Inflation. These became over- and underdensities which evolved into voids and galaxies. When it comes to wealth transfer, gravity doesn‘t miss a trick. The first structures to form were giant sheets that walled the emptying voids. The sheets unwove into filaments. The filament crisscrossed and joined, and in their junction points, supergalaxy clusters came to be. Today, the long strings of galaxy clusters that connect the filaments are nourished by gigantic, tenuous rivers moving gas out of voids and into galaxies. The tenuity of a filament is boggling—only one or two atoms in a cubic meter. Filaments compensate for their tenuity with immensity. Disks accrete gas directly from their filament and inherit its angular momentum. Gas dissipates its internal motions and coheres into a smooth flow with the net angular momentum appearing as a systematic rotation moment imparted to the galaxy disc. At hundreds of kilometers per second, the flow out of a filament wouldn’t riffle the tips of a feather, yet it transmits enough angular momentum to keep an entire galaxy cluster in full spin.

All this lyricism on the charms along the byways of Hubble time changes not one iota of how we live here and now. How DO we fill our Milky Way’s gas tank on the long route to the Virgo Supercluster?

Like everybody else: we stop at the gas station.

(See Fig. 7 below to know what they look like.)

Fig. 7. Computer simulations of cosmic filamentary infall into galaxy clusters. Each segment depicts the patterns of energy flow resulting from different sets of parameters. Squint your eyes a bit and you just might see our Milky Way at one of the pump islands. Source: Sanchez Almeida et al. 2014, amending original sims by Fumagalli et al. 2011b Fig. 6.

At the petrol pump on the way to Virgo, you’ll be there awhile. Say, 2.6 billion years. The highway to Virgo passes some magnificent scenery. We and our telescopes can only see a single percent of all it shows, the visible spectrum. Ninety-nine percent of the electromagnetic spectrum is invisible to our eyes. If you want to see the passing landscape in full, visit Illustris 1 & 2 and the EAGLE sims.

(See Fig 8 below)

Fig. 8. On the road again. Here’s the map. Libeskind 2015.

Time for the wrap. All this lyricism on the charms along the byways of Hubble time changes not one whit of here and now. Midnight. Scope’s cooled. Clear night. Antares up. The red heart of Scorpius forms claws and a sting into a galaxy spinning star after star into core and more core. One day its time too will be up. An incandescent unsheathing of light bright enough to be seen to the end of thought. Then core, core and only more core, till someday timeoutofmind from now that too will be no more.

Uh-ohhh . . . Tank’s empty.

Now what?
Attached Thumbnails
Click for full-size image (Fig 7 Cosmic inflow fm intergalactic filaments, Fumagalli 2011b Fig 6 MNRAS.jpg)
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Click for full-size image (Fig 8 Libeskind, cosmic gas flow from Local Void to Virgo Supercluster.jpg)
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Old 18-05-2016, 06:25 PM
Bombardon (Eugene)
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Again, beautiful reports, Dana, bringing complex concepts within the scope of all star- seekers who stretch the limits of their own scopes and leave us always on the edge of searching for what lies beyond. I have spent the odd hour over many years searching for and often not finding those faint fuzzies as my own mental gas tanks hovers near empty!
I often wonder why we don’t head for the obvious beacons that eventually stand out like searchlights to our dark adjusted eyes. You reported passing the obvious Antares and not even bowing to that glaring urchin in orange lederhosen that only wakes from obscurity ever couple of years and then rapidly hides under its eccentric blanket.
Thanks, Dana, for taking us on the road not taken, and beware your preoccupation with the Southern Pleiades – you make grow to like this pretender, which carries Otto Struve’s Grecian signature. Regards, Eugene
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