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Huge Hydrogen Cloud Will Hit Milky Way
diewlasing points us to a story about a hydrogen cloud, eleven thousand light-years long, which will collide with the Milky Way in a devastating crossfire of shock waves and star formation...in 20-40 million years. Mark your calendars. At least it will give us something to watch while we're waiting for Andromeda to hit us in a few billion years. Hopefully, it will look at least this cool.
"The detailed GBT study dramatically changed the astronomers' understanding of the cloud. Its velocity shows that it is falling into the Milky Way, not leaving it, and the new data show that it is plowing up Milky Way gas before it as it falls. 'Its shape, somewhat similar to that of a comet, indicates that it's already hitting gas in our Galaxy's outskirts,' Lockman said. 'It is also feeling a tidal force from the gravity of the Milky Way and may be in the process of being torn apart. Our Galaxy will get a rain of gas from this cloud, then in about 20 to 40 million years, the cloud's core will smash into the Milky Way's plane,' Lockman explained."
It seems to me that something with enough gas to create 1M stars akin to the Sun might have a noticeable impact on the revolutionary nature of the galaxy. Nothing astounding, probably akin to the added wobble of the Earth after the giant 2004 earthquake (the one that caused the tsunami) but it's probably something that, on the off chance we or some other life form is around, would be really awesome to observe. Also, assuming we don't have all the answers yet, seeing how the galaxy responds to such a sudden, massive change compared to our models could really tell us exactly how much mass there is, how it's distributed, etc.
I live in constant fear of the Coming of the Red Spiders.
Hey, that's just the fuel we'll need for a Bussard ramjet
Maybe people who don't understand what will happen will have a problem. Like the kind of people that think they will simply pass through each other. What really happens is that colliding clouds form a shock front and can heat up to millions of degrees C.
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
I think the question that the original poster raised is best expressed as, "can someone give a description of this 'gas cloud' in terms of average units of mass per units of volume?" And perhaps adding in "what is the total volume of this cloud, if we consider the boundary of the cloud as the zone where local mass-per-unit-volume descends to 10% of average mass-per-unit-volume?" While your point may be technically correct, talking about a temperature of millions of degrees C for such a sparse cloud would mislead exactly the same people you're feeling superior towards, and they'll assume it's some sort of intergalactic lava flow.
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So this "collision" will be quite soft in terms of energy density: One feather landing on an area the size of the earth.
Right at first, yes. But there will be collisions, there will be gravity interaction.
There also is the fact that (1000000 suns x 2e30 kg = 2e37 kg) of mass coming in at 150 miles/second contain a *lot* of energy...
Some of that mass will combine with the gas in milkyway and push some areas over the threshold into collapsing and forming stars.
Hope this helps ;-)
Ulli
P.S.: I might have gotten confused with the numbers for the suns...
Simple things should be simple, complex things should be possible.
Does anyone else have a problem with the word "smashing" to describe the contact of two bits of not-quite-vacuum passing through each other?
I don't. (At least not until I find out the relative masses and densities of the gas cloud vs. both the sections of the Milky Way it's about to encounter and the interstellar-gas components of them.)
The cloud may be a very hard vacuum - only slightly softer than the intergalactic space around it. But at galactic scales it still amounts to something quite dense and massive, which will not pass through the interstellar gas and solar winds of our galaxy without interacting repeatedly - let alone through the magnetic fields of the galaxy and the stars and planets that compose it.
I'd expect it to coalesce with the galaxy. That much mass at that much relative velocity will dump enormous amounts of energy into compression and heat at the shock front (similar to the graduation of "falling pebble" to something akin to a bomb when the pebble is falling at cometary speed, or a nuclear bomb when the "pebble" is also a couple miles in diameter). The energy density might be small, but over half the sky the radiant temperature can add up. Over that much matter, even at near-vacuum densities, even fusion events could be non-trivial - especially since magnetic effects could produce concentrations.
In gas clouds I'd expect it, at a minimum, to kick off a round of star formation. Also to sweep the gas and dust out from between existing stars and their planetary systems (and fractionate it), as dense accumulations are accellerated little while gas and dust encounter something of comparable density.
Even if the density is so low that the above effects aren't significant for planetary systems like ours, the passage of the cloud (especially the shock front) would wreak non-trivial havoc on the solar wind and magnetosphere - and thus planetary radiation shielding. Because the solar wind -> radiation shielding -> water condensation nucleation -> cloud cover -> solar heat reflection connection seems to be a major contributor to (geologically) short-term planetary temperature changes, the arrival and passage of the gas cloud could have a major effect on climate. (Even if its impact on the magnetosphere doesn't "stir up" some change in activity on the solar surface or modify the sunspot cycle.)
Which brings up the questions:
- Have similar events occurred in the geologically "recent" past?
- If so, do they have any relation to ice ages and interglacial periods or to mass extinction events?
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
If a cloud of oxygen of the same size were to come at the Milky Way from the opposite size, would the resulting cloud of water be enough to put out all of the stars?
The Spice Must Flow!