Distant Dusty Galaxy

Astronomers at ALMA and VLT have discovered the most distant dusty galaxy ever observed! (As opposed to the most dusty distant galaxy, although that’s a more subjective superlative.) In their paper released today in Astrophysical Journal Letters, the group discussed their observations of this incredibly distant galaxy and what it could mean for furthering our understanding of the early Universe.

This galaxy, called A2744_YD4, is the youngest and most remote galaxy ever observed by ALMA. Any time we look at objects in space, we also look back in time, since all light travels at the same cosmic speed limit and must cross enormous distances to get to us. This particular observation is looking back in time to when the Universe was only about 600 million years old, a mere four percent of its present age! After a dreary period known as the Cosmic Dark Ages, the earliest stars and galaxies were still in the midst of reionizing the Universe (no small task).

Seeing so far back in time and space is very difficult, and in this case, gravitational lensingplayedakeyroleingivingastronomersadeeperlookbackintime. Before discovering A2744_YD4, astronomers were studying the galaxy cluster Abell 2744. Abell 2744 gravitationally lensed the image of the much more distant A2744_YD4 and magnified it by about 1.8 times, allowing the team to see more easily into the remote past. What they found was a surprisingly dusty young galaxy, containing a mass of dust equivalent to around six million Suns.

All that dust is what makes this observation a big deal. When astronomers refer to dust, they are usually referring to interstellar dust, composed of heavy elements, such as silicon, carbon, and aluminum. “Not only is A2744_YD4 the most distant galaxy yet observed by ALMA,” comments Nicolas Laporte, leader of the study, “but the detection of so much dust indicates early supernovae must have already polluted this galaxy.” Space dust can only be present if massive stars have already lived, died, and released their material into their surroundings. This is because all heavy elements are formed inside stars through nuclear fusion or during supernovae explosions. So if we’re seeing a dusty galaxy in the early Universe, that suggests that the earliest stars and galaxies had already formed (and even died), shedding light on an area of astronomy that is still not fully understood (they don’t call ’em the “dark ages” for nothing).

In addition to being the earliest and most distant dusty galaxy, A2744_YD4 contains ionized oxygen, the earliest we’ve ever seen. ALMA observed oxygen back in June 2016 from a galaxy that was around when the Universe was only about 700 million years old.

“Further measurements of this kind offer the exciting prospect of tracing early star formation and the creation of the heavier chemical elements even further back into the early Universe.” Our planet wouldn’t be here without the heavy elements and dust that are present in our galaxy, and humans certainly wouldn’t be here without oxygen. By understanding how these early galaxies form, we can further understand our own cosmic origins.

Image Credit: ESO

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