The Creation of a Galactic Metropolis
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.