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When Galaxies Collide, Black Holes Don’t Always Get the Feast They Were Hoping for

What happens when galaxies collide? Well, if any humans are around in about a billion years, they might find out. That’s when our Milky Way galaxy is scheduled to collide with our neighbour the Andromeda galaxy. That event will be an epic, titanic, collision. The supermassive black holes at the center of both galaxies will feast on new material and flare brightly as the collision brings more gas and dust within reach of their overwhelming gravitational pull. Where massive giant stars collide with each other, lighting up the skies and spraying deadly radiation everywhere. Right?

Maybe not. In fact, there might be no feasting at all, and hardly anything titanic about it.

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An Active Galaxy That Erupts Predictably Every 114 Days Or So

Computers are known for their ability to spot patterns.  It’s what they are good at, and over the last 50+ years they have continued to improve.  But they only know how to spot patterns if they know where to look for them in data.  So sometimes, it falls to a human to truly see a pattern that no one expected to be there.

That is exactly what happened in the case of the discovery of the most consistent active galaxy yet discovered.  Anna Payne, a graduate student at the University of Hawai’i at Manoa, was looking into data collected by the All Sky Automated Survey for Supernovae (ASAS-SN), and notice a strange feature about one of its galaxies, known as ESO 253-3: it was getting significantly brighter every 114 days.

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The Universe in Formation. Hubble Sees 6 Examples of Merging Galaxies

Audio narration by the author is available above

10 billion years ago, galaxies of the Universe were ablaze with the light of newly forming stars. This epic phase of history is known as  “Cosmic Noon” – the height of all star creation. Galaxies like our Milky Way aren’t creating stars at nearly the rates they were in the ancient past. However, there is a time when galaxies in the present can explode with star formation – when they collide with each other. This recently published collage of merging galaxies by the Hubble HiPEEC survey (Hubble imaging Probe of Extreme Environments and Clusters) highlights six of these collisions which help us understand star formation in the early Universe.

Newly released collage of six galaxy mergers used in the HiPEEC survey.
Top Row Left to Right: NGC 3256, 1614, 4195 Bottom Row Left To Right: NGC 3690, 6052, 34
– Credit ESA/Hubble/NASA
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This is the Fireworks Galaxy. It’s had ten Supernovae in the Last Century Alone

Say hello to NGC 6946, otherwise known as the Fireworks Galaxy. This little galaxy is the most prolific producer of supernovae in the known universe, popping off those incredible explosions roughly once a decade. It’s secret? An incredibly high rate of star formation.

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This galaxy took only 500 million years to form

Galaxies are supposed to build up a very slowly, taking billions of years to acquire their vast bulk. But a newfound galaxy, appearing in the universe when it was only 1.8 billion years old, tells a different tale. It formed stars at a rate hundreds of times greater than the Milky Way, and was able to build itself up to host 200 billion stars in less than 500 million years – perhaps the universe’s greatest speed run.

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A Galaxy is Making New Stars Faster Than its Black Hole Can Starve Them for Fuel

A monster lurks at the heart of many galaxies – even our own Milky Way. This monster possesses the mass of millions or billions of Suns. Immense gravity shrouds it within a dark cocoon of space and time – a supermassive black hole. But while hidden in darkness and difficult to observe, black holes can also shine brighter than an entire galaxy. When feeding, these sleeping monsters awaken transforming into a quasar – one of the Universe’s most luminous objects. The energy a quasar radiates into space is so powerful, it can interfere with star formation for thousands of light years across their host galaxies. But one galaxy appears to be winning a struggle against its awoken blazing monster and in a recent paper published in the Astrophysical Journal, astronomers are trying to determine how this galaxy survives.

Animation of Interstellar Matter Falling into a Black Hole Creating a Quasar – ESA
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The Spherical Structure at the Core of the Milky Way Formed in a Single Burst of Star Formation

Like other spiral galaxies, the Milky Way has a bulging sphere of stars in its center. It’s called “The Bulge,” and it’s roughly 10,000 light-years in radius. Astronomers have debated the bulge’s origins, with some research showing that multiple episodes of star formation created it.

But a new survey with the NOIRLab’s Dark Energy Camera suggests that one single epic burst of star formation created the bulge over 10 billion years ago.

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Galaxies Grew Quickly and Early On in the Universe

The behaviour of galaxies in the early Universe attracts a lot of attention from researchers. In fact, everything about the early Universe is under intense scientific scrutiny for obvious reasons. But unlike the Universe’s first stars, which have all died long ago, the galaxies we see around us—including our own—have been here since the early days.

Current scientific thinking says that in the early days of the Universe, the galaxies grew slowly, taking billions of years to become what they are now. But new observations show that might not be the case.

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