The Atacama Large Millimeter/submillimeter Array (ALMA) has succeeded in imaging star formation regions in a distant galaxy, with a resolution six times greater than that achievable by the Hubble Space Telescope. The galaxy, dubbed HATLAS J090311.6+003906 or SDP.81, would ordinarily be far too distant to be observed in such impressive detail. However, thanks to an amazing cosmic coincidence, it has fallen foul of a phenomenon known as gravitational lensing, which essentially grants astronomers the opportunity to gaze into the distant past.
First predicted by Albert Einstein as an element of his theory of general relativity, gravitational lensing occurs when a nearby galaxy is perfectly aligned between a more distant galaxy and Earth. This nearby galaxy has the effect of warping spacetime, and any light emitted from the more distant galaxy would pass through this lensing effect, becoming greatly magnified, but also heavily distorted in the process.
Thankfully, astronomers now have tools that allow them to heavily minimize the detrimental effects of gravitational lensing. This particular class of gravitational lens is known as an Einstein ring. The faintness of the center of the image acts as an indicator for the mass of the celestial object that eclipses it. Based on the fact that the center of SDP.81's image is essentially invisible, it is believed that the foreground galaxy hosts a supermassive black hole at its heart, 200 - 300 million times the mass of the Sun.
In order to make the most of the lensing effect, the 66 high-precision antennas that make up ALMA were separated by 15 km (9.3 miles), providing the greatest possible detail.
These factors working in concert have allowed astronomers to view the distant galaxy as it was 2.4 billion years after the Big Bang, when the Universe was only 15 percent its present age. It is estimated that the light from SDP.81 took 11.4 billion years to reach us, allowing astronomers to observe instances of ancient star formation.
By examining the spectral characteristics of SND.81, astronomers have been able to estimate the galaxy's mass and rotation. We can see vast clouds of gas collapsing inward, ready to explode into regions of fierce star formation. Furthermore, the clarity of the data returned by ALMA is such that astronomers were able to pick out a number of massive, active stellar formation regions down to a scale of 200 light-years that share many characteristics with the famous Orion Nebula.
"The reconstructed ALMA image of the galaxy is spectacular," states Rob Ivison, ESO’s Director for Science and co-author of two of the papers on the findings. "ALMA’s huge collecting area, the large separation of its antennas, and the stable atmosphere above the Atacama desert all lead to exquisite detail in both images and spectra. That means that we get very sensitive observations, as well as information about how the different parts of the galaxy are moving. We can study galaxies at the other end of the Universe as they merge and create huge numbers of stars. This is the kind of stuff that gets me up in the morning."
The video below courtesy of ESO displays how light from a distant background galaxy is distorted by the foreground galaxy.
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