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Lifting the Veil on the Early Universe

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The Creation of a Galactic Metropolis

An artist’s conception of a giant protocluster of galaxies forming in the early universe. The galaxies are busy forming new stars while at the same time interacting with each other. Courtesy: ESO/M. Kornmesser

From time to time astronomers give us a peek at the early universe and each time they do, they lift the veil on earlier and earlier time periods of our cosmic history. In recent years, they’ve shown us early “shreds” of galaxies and hints of the first stars to ever form. Galaxies began forming some 500 million years after the Big Bang occurred. As galaxies formed through collision and cannibalism, they also clumped together in clusters. One of the oldest clusters is called the Spiderweb Galaxy (or MTC1138-262) is at the heart of a galactic protocluster that began assembling more than 10 billion years ago.

Astronomers interested in star formation in infant galaxies during those early epochs of galaxy building took a closer look at this cluster using the APEX Telescope in Chile, part of the European Southern Observatory. This telescope is exquisitely sensitive to millimeter wavelengths of light (part of the infrared spectrum of light).  It opens a window on distant universe, allowing astronomers to look for faint glimmers of energy from the early universe. They used something called the LABOCA (which stands for Large Bolometer Camera) instrument to look at the cluster. This camera is essentially a sensitive thermometer that helps astronomers sense any kind of heat above absolute zero.  That means it can detect the glimmers of star formation from the early universe, even if they’re hidden by clouds of dust and gas.

Essentially, the APEX telescope and instruments revealed that there are many more sources of star formation in the region of the Spiderweb than astronomers suspected. Their ability to peek behind the veil of dust that hid parts of the cluster’s activity showed astronomers something of a surprise. Yes, star formation is happening there, growing in the interacting galaxies. But, it is  not where they expected it to be. It’s clustered in a relatively small region of the cluster, and not in filaments of gas and dust strung between the member galaxies, where such events usually occur as galaxies interact. Galaxy collisions regularly set off bursts of star formation, and you often see bluish starburst knots strung out between member galaxies like strings of fuzzy pearls.

So, why is star birth so constrained to a smallish, non-central area of the cluster? Good question. Finding the star formation is great news, but now astronomers need to figure out why it’s occurring in a region where they didn’t expect it to be. What processes are shaping the starbirth nurseries in this cluster? Do they tell us something about how clusters formed in the early universe?  Good questions, which astronomers hope to answer by focusing the massed ALMA array on the region when they get a chance. It should give them nicely resolved looks at the stellar creches in the Spiderweb Galaxy and its siblings in the cluster.

 

 

 

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We Come From the Stars

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This is Our Home Galaxy, and a Couple of Neighbors

As the Milky Way rises over the horizon at the European Southern Observatory, its companion galaxies also come into view. The Large Magellanic Cloud (LMC) at far left lies about 160,000 light-years away, while the Small Magellanic Cloud (SMC, above and to the right of the LMC) lies about 200,000 light-years away. New simulations show that the LMC stole stars from the SMC when the two galaxies collided 300 million years ago. Microlensing events that have been observed are due to LMC stars passing in front of a stream of stars pulled from the SMC.
Credit: ESO/Y. Beletsky

When you look out at the night sky, you’re looking at our ancient home. Yes, Earth is our current home. But, in the grand scheme of things, the galaxy — and all the elements that make it are also our home.  The elements that make up our bodies, our planets, and our star all were either created in the Big Bang (hydrogen, for example), or inside other stars (carbon, oxygen, nitrogen, etc.).  Multiple generations of stars have lived and died in the galaxy, and we are the resulting “star stuff”.

But, there’s more than star stuff out there.  There are mysterious things that may tell astronomers more about types of matter in the cosmos and distribution of that matter throughout the universe.

Astronomers have been studying one of those two irregular-looking clouds of stars that appear just below our galaxy in this image to understand a category of objects called MACHO (Massive Compact Halo Objects). These were thought to be things about the mass of a star that were so faint they couldn’t be easily detected. Surveys of this region of our galactic neighborhood have been underway to see if MACHOs could be part of that mysterious collection of “stuff” called “dark matter” that seems to be an incredibly important part of the universe.

In order for MACHOs to make up dark matter, they must be very faint. To even decide if they’re “there”, astronomers looked for a phenomenon known as microlensing. During a microlensing event, a nearby object passes in front of a more distant star. The gravity of the closer object bends light from the star like a lens, magnifying it and causing it to brighten. If a MACHO does this, then they’d know a little bit more about the object.

By studying the LMC, astronomers hoped to see MACHOs within the Milky Way lensing distant LMC stars. The number of microlensing events observed by various teams was smaller than needed to account for dark matter, but much higher than expected from the known population of stars in the Milky Way. This left the origin of the observed events a puzzle and the existence of MACHOs as exotic objects a possibility.

Instead of MACHOs, a trail of stars removed from the SMC could well be responsible for the microlensing events. How do astronomers know this? They’ve done computer simulations showing that the most likely explanation for the observed microlensing events was an unseen population of stars removed by the LMC from its companion, the SMC. Foreground stars in the LMC are gravitationally lensing the trail of removed stars located behind the LMC from our point of view.

Although the evidence for the trail of lensed stars is persuasive, they haven’t been directly observed yet. That will take time, since these could be faint. A number of teams are searching for the signatures of these stars within a bridge of gas that connects the Magellanic Clouds. The computer models used to simulate the trail will point the way for astronomers to find the other “stuff” that makes up the galaxies… and intergalactic space.