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Massive disk galaxy could change our understanding of how galaxies are born

A massive, rotating disk galaxy that first formed just 1.5 billion years after the Big Bang, could upend our understanding of galaxy formation, scientists suggest in a new study. 

In traditional galaxy formation models and according to modern cosmology, galaxies are built beginning with dark-matter halos. Over time, those halos pull in gases and material, eventually building up full-fledged galaxies. Disk galaxies, like our own Milky Way, form with prominent disks of stars and gas and are thought to be created in a method known as "hot mode" galaxy formation, where gas falls inward toward the galaxy's central region where it then cools and condenses. 

This process is thought to be fairly gradual, taking a long time. But the newly discovered galaxy DLA0817g, nicknamed the "Wolfe Disk," which scientists believe formed in the early universe, suggests that disk galaxies could actually form quite quickly. 

Related: Milky Way Quiz: Test Your Galaxy Smarts

An artist's impression of the Wolfe Disk, a massive disk galaxy in the early universe.

An artist's impression of the Wolfe Disk, a massive disk galaxy in the early universe. (Image credit: NRAO/AUI/NSF, S. Dagnello)

In a new study led by Marcel Neeleman of the Max Planck Institute for Astronomy in Germany, researchers spotted the Wolfe Disk using ALMA, the Atacama Large Millimeter/submillimeter Array in Chile. They found out that the object was a large, stable rotating disk, clocking in at a whopping 70 billion times the mass of our sun.

In the new observations, the disk appears as it was when the universe was just 1.5 billion years old, or 10% of its current age. The disk appears extremely massive and stable for something so young. So how could such a massive galaxy form so quickly, so early in the universe? 

Researchers suggest that the galaxy might have formed by a process known as "cold-mode accretion." They think that the gas falling in towards the galaxy's center was actually cold so, because the gas didn't need time to cool down as it approached the galactic center, the disk was able to more rapidly condense. 

"The result provides valuable input for a present-day discussion about how galaxies form," according to a statement from the Max Planck Institute. 

However, astrophysicist Alfred Tiley noted in a Nature News & Views article accompanying this study, these findings are based off of a single galaxy. He emphasized that more similar observations would be needed to validate this hypothesis. 

This work was published Wednesday (May 20) in the journal Nature.  

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  • Ogamol
    Or up end our estimates of what happened when in our Big Bang timeline. (My "favorite" Big Bang hypothesis: 'the universe was expanding at speed X for a long time after the initial "Bang", then spontaneously slowed down. Just accept it.' Yes, I'm aware that the size discrepancies between continued maximum expansion and visible expansion now are immense. I just don't accept the magical "Suddenly, it changed .". )

    (As I have only recently (past 60 days) considered what nearly-even mass distribution means in a constantly expanding universe, I'll not toss that into the mix.)
    Reply
  • TorbjornLarsson
    The cold gas pathway, where the gas streams along the cosmic filaments without collisions, is interesting. Tiley is correct that this result is not robust but need repetition, but the method used implies this type of galaxy should be common - they had to use background quasar galaxies to observe early non-quasar galaxies by absorbed light, and they were only up to 6 found galaxy candidates when they found the Wolfe disk.
    Reply
  • TorbjornLarsson
    Ogamol said:

    Or up end our estimates of what happened when in our Big Bang timeline. (My "favorite" Big Bang hypothesis: 'the universe was expanding at speed X for a long time after the initial "Bang", then spontaneously slowed down. Just accept it.' Yes, I'm aware that the size discrepancies between continued maximum expansion and visible expansion now are immense. I just don't accept the magical "Suddenly, it changed .". )

    Yes, it could move (early galaxies have already moved) the timeline somewhat.

    As for the rest of the comment, I'm not sure what you mean. 'Magical' is poor terminology for something that is mainstream cosmology - the Lambda Cold Dark Matter model in it's modern, self consistent, inflationary big bang form - and where main processes are fairly well understood and parameters are tested to within 0.1 % uncertainty. The cosmological expansion rate is understood to be described by Einstein's equations for the underlying general relativistic Friedmann–Lemaître–Robertson–Walker universe. (Which, yes, suffice to approximate the mass energy content as a homogeneous "liquid" density. Until you want to describe the initially 10^-5 parts variation that shows up in the cosmic background spectra and later as cosmic filaments, where you need to switch to "gas" particles to do analysis and simulations.)

    Long story short, the expansion rate in a FLRW universe with energy and pressure variables is decided by its inner state, akin to a pressure vessel. This is described in Cosmology 101 courses, which you may be interested in studying if you are amazed by the changes. (I recommend Susskind's free Stanford MOOC's, or you could watch some PBS Space & Time videos. But before you do that you may enjoy the overview video I link to later in this comment.)

    During the initial era of inflation the expansion is decided by the inflation field potential energy, so being constant energy density the universe expanded exponentially, and being immense energy it expanded immensely fast. After our universe ended its slow roll inflation*, the inflation field energy was released in the hot big bang, and we see inner state change and the expansion rate change accordingly to much slower rates of expansion**.

    * This ending is not by magic but natural though conceptually complicated. Essentially inflation is a process where a system - the universe - rolls down a hill of a Higgs like scalar field. The quantum fluctuations of the field kicks some volumes down the hill to end faster and some volumes up the hill to continue - but the main point is that an exponentially increasing volume is stuck in inflation while some local universe volumes enter their hot big bang era https://www.forbes.com/sites/startswithabang/2018/06/27/what-was-it-like-when-the-universe-was-inflating/ ].



    https://thumbor.forbes.com/thumbor/711x1153/https://blogs-images.forbes.com/startswithabang/files/2016/11/0-usFTRCwYVh5kZcP2.jpg?width=960
    Inflation ends (top) when a ball rolls into the valley. But the inflationary field is a quantum one (middle), spreading out over time, and taking on different values in different regions of inflating space. While many regions of space (purple, red and cyan) will see inflation end, many more (green, blue) will see inflation continue, potentially for an eternity (bottom). ]

    No magic, just process.

    ** If you want a quick summary of the expansion rate changes, after inflation the hot big bang starts with a radiation dominated era - no matter yet - and then a matter dominated era - radiation becomes too diluted by expansion. Both of those expands sub-exponentially somewhat like if you throw a mass (or energy) "ball" against gravity, so the expansion rates look akin to parables. But radiation becomes stretched by expansion so expands somewhat differently than matter. After a longer while both energy and matter becomes so dilute that the constant energy density dark, vacuum energy starts to dominate, and again the expansion rates becomes exponential as it was under inflation.

    An overview video, which doesn't describe the expansion rate changes but the inner state changes and is a convenient orientation to grok the modern inflationary big bang universe:

    P1Q8tS-9hYoView: https://www.youtube.com/watch?v=P1Q8tS-9hYo
    Reply
  • Ogamol
    Cool.
    Reply