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Monsters Gobble Galaxies to Grow

In the direction of the constellation Canis Major, some 55 million light years from Earth, two  galaxies appear to be at the beginning stages of a merger that has been captured by the Hubble Space Telescope and its Wide Field Planetary Camera 2. Credit: NASA/ESA and The Hubble Heritage Team (STScI)
In the constellation Canis Major, some 55 million light-years from Earth, two galaxies begin a merger. Courtesy of 
NASA/ESA and the Hubble Heritage Team (STScI)

When it comes to galaxies, it’s survival of the largest. Monster galaxies grow by cannibalizing their smaller neighbors, instead of birthing new stars on their own.

In a new study, led by Aaron Robotham of the University of Western Australia, that looked at 22,000 galaxies, astronomers found that the more massive the galaxy, the more it grows in size by gobbling up their smaller “dwarf” counterparts.

“All galaxies start off small and grow by collecting gas and quite efficiently turning it into stars,” said Robotham in a press statement“Then every now and then they get completely cannibalized by some much larger galaxy.”

This galactic cannibalism appears to be self-perpetuating, since as the galaxies grow they gain more gravitational strength and therefore more easily pull in their neighbors, according the study released this month in the journal Monthly Notices of the Royal Astronomical Society.

And it turns out our own home galaxy, the Milky Way, may now be tipping the scale on the obese side—growing only by snacking on wayward islands of stars.

“The Milky Way hasn’t merged with another large galaxy for a long time, but you can still see remnants of all the old galaxies we’ve cannibalized,” Robotham explained.

“We’re also going to eat two nearby dwarf galaxies, the Large and Small Magellanic Clouds, in about four billion years.”

Andromeda Big Bully

What goes around comes around, however, and the Milky Way too may fall victim to galactic cannibalization. Our neighbor, the Andromeda galaxy, now some 2.6 million light-years away from Earth, will likely approach and devour the Milky Way in about five billion years.

“Technically, Andromeda will eat us because it’s the more massive one,” Robotham said.

This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth's night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger
This illustration shows a stage in the predicted merger between the Milky Way and Andromeda galaxies. In this image, representing Earth’s night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. Courtesy of NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger

Eventually, a similar fate may await most monster galaxies. At one point in the distant future, the cluster members will slowly merge together into only a few supercolossal galaxies that will end up dominating the cosmos.

“If you waited a really, really, really long time, that would eventually happen, but by really long I mean many times the age of the universe,” which is about 13.8 billion years old, said Robotham.

See for Yourself

Even if you can’t wait for the Milky Way merger, other opportunities abound to see galactic smashups. One of the best examples of interacting galaxies is the famous Whirlpool galaxy in the northern constellation Canes Venatici. It is a small stellar pattern just beside the famous constellation Ursa Major, the Great Bear.

This image of the Whirlpool galaxy was captured using the WIYN 3.5-m telescope on Kitt Peak, Arizona. Credit: K. Rhode, M. Young and WIYN/NOAO/AURA/NSF
This image of the Whirlpool galaxy was captured using the WIYN 3.5-meter telescope on Kitt Peak, Arizona. Credit: K. Rhode, M. Young, and WIYN/NOAO/AURA/NSF

Visible with small telescopes throughout the Northern Hemisphere, the Whirlpool galaxy, also known as Messier 51, is a spiral galaxy that has a visible bridge of gas, dust, and stars that connect it to a smaller, irregular galaxy known as NGC 5195.

Under dark skies you may even be able to glimpse the magnitude 8.4 galaxy with binoculars.

This starchart shows the location of the Whirlpool galaxy (M51) just underneath Alkaid - the last star in the handle of the Big Dipper as seen in the early evenings of September. Credit: SkySafari
This star chart shows the location of the Whirlpool galaxy (M51) just underneath Alkaid, the last star in the handle of the Big Dipper as seen in the early evenings of September. Credit: SkySafari

You can find M51 by looking 3.5 degrees southeast of the star Alkaid. Alkaid marks the end of the handle of the Big Dipper.

The Whirlpool is estimated to contain over 150 billion stars, making it at least as massive as our own Milky Way.

While you watch, ponder the amazing fact that its ghostly pinwheel structure sits a whopping 27 million light-years away from Earth.

Happy hunting!

Follow Andrew Fazekas, the Night Sky Guy, on Twitter and Facebook.

Comments

  1. Mathew panamkat
    Delhi
    October 25, 2014, 2:38 am

    Much before that happens mankind would have gone to its ultimate destination.

  2. Justin Tang
    Malaysia
    September 26, 2014, 11:03 pm

    Hope for a clear sky then.

  3. ramp
    September 26, 2014, 5:04 pm

    @BryteGee Humans survive for 5 billion years? The Earth itself should theoretically be gone by then–with the death of the sun.

    Realistically though, humans ain’t surviving that long

  4. Anthony
    September 25, 2014, 9:06 pm

    THANKS! Needed for homework! Interesting also. Hopefully we will get bigger than the other galaxys before Andromeda ever hits us. Thank the stars.

  5. Alekz Lopez
    México D.F. tulyehualco xochimilco
    September 25, 2014, 6:36 pm

    La investigación está increíble me agrado mucho, sobre todo la cantidad de energía en el momento del canibalismo de la más grande a la desafortunada galaxia. Inimaginables acontecimientos suceden y lo pequeño que es nuestro planeta, que grande es el poder del o de los que crean todo este movimiento. Estoy muy impresionado (*◇*)

  6. Haily
    Baltimore
    September 25, 2014, 1:19 pm

    Thanks For The Article I Needed An Article For My Homework And This Is Incredibly Detailed By The Way Thanks Again! 🙂

  7. Richard Harry Dickson
    September 25, 2014, 12:26 pm

    So it’s like, if I took a small rat and fused into my chest, my chest may look a little strange, but my overall shape remains the same… interesting.

  8. BryteGee
    Beijing
    September 25, 2014, 1:23 am

    According to a documentary “Cosmos: A Space & Time Odyssey”, although the collision between Andromeda and our Milky way is inevitable, due to large space between planets and stars, the collision between spacing objects seems to be in quite small a chance. so if human beings can endure long enough, we can see the magnificent night sky as Figure 2 illustrated. Envy our offsprings