Astronomers have identified a new candidate for the title of “most distant object ever seen in the universe”. By combining the power of NASA’s Hubble and Spitzer space telescopes, researchers identified the object as a small far-away galaxy only 600 light-years wide, a tiny fraction of the size of our own 150,000 light-years wide Milky Way.
The galaxy, named MACS0647-JD, was observed 420 million years after the big bang, and its light has traveled 13.3 billion years to reach Earth. The discovery comes thanks to the Cluster Lensing And Supernova Survey with Hubble (CLASH) program, which couples the gravitational lensing power of 25 massive galaxy clusters with Hubble’s newly enhanced panchromatic imaging capabilities (Wide Field Camera 3 and the restored Advanced Camera for Surveys). The international group carrying out the CLASH program, led by Marc Postman of the Space Telescope Science Institute in Baltimore, Md., is using massive galaxy clusters as cosmic telescopes to magnify distant galaxies behind them. The effect essentially uses those galaxy clusters as natural zoom lenses to enhance Hubble’s ability to see further into the cosmos than anyone could have ever imagined.
The light from MACS0647-JD traveled through the universe for 8 billion years before taking a detour along several paths around the massive galaxy cluster MACS J0647+7015, the cluster responsible for magnifying the light from MACS0647-JD and allowing CLASH researchers to see what Hubble alone could not. Without the natural magnification powers of MACS J0647+7015, astronomers simply would not have been able to see this remote galaxy.
“This cluster does what no man-made telescope can do,” said Postman. “Without the magnification, it would require a Herculean effort to observe this galaxy.”
The newly discovered galaxy, named MACS0647-JD, is very young and only a tiny fraction of the size of our Milky Way. The object is observed 420 million years after the big bang. Video Credit: NASA, ESA, and G. Bacon (STScI), Youtube Credit: NASAexplore.
The galaxy is in fact so small that researchers believe it to be in the infancy of its formation, the first steps of forming a larger galaxy. “This object may be one of many building blocks of a galaxy,” said CLASH team member and the study’s lead author, Dan Coe of the Space Telescope Science Institute. “Over the next 13 billion years, it may have dozens, hundreds, or even thousands of merging events with other galaxies and galaxy fragments.”
Coe discovered the galaxy last February while going over a catalogue of thousands of gravitationally lensed objects found in Hubble observations. The galaxy was observed with 17 filters, spanning near-ultraviolet to near-infrared wavelengths, using Hubble’s Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS). The galaxy, however, only appeared in the two reddest filters.
“So either MACS0647-JD is a very red object, only shining at red wavelengths, or it is extremely distant and its light has been ‘redshifted’ to these wavelengths, or some combination of the two,” Coe said.
Redshift is a consequence of the expansion of space over cosmic time. Astronomers study the distant universe in near-infrared light because the expansion of space stretches ultraviolet and visible light from galaxies into infrared wavelengths. Coe estimates MACS0647-JD has a redshift of 11, the highest ever observed.
Coe and his colleagues spent months systematically ruling out other possible explanations for the identity of MACS0647-JD. Red stars, brown dwarfs, and red (old or dusty) galaxies at intermediate distances from Earth were all possibilities. The CLASH team identified eight galaxies lensed by galaxy cluster MACS J0647+7015, and used the positions of those eight galaxies to produce a map of the cluster’s mass, which is primarily composed of dark matter – the invisible form of matter that makes up the bulk of the universe.
“It’s like a big puzzle,” said Coe. “We have to arrange the mass in the cluster so that it deflects the light of each galaxy to the positions observed.” Thorough analysis revealed that the cluster’s mass distribution produced three lensed images of MACS0647-JD at the positions and relative brightness observed in the Hubble image, leading to the conclusion that a very distant galaxy was the correct explanation.
“All three of the lensed galaxy images match fairly well and are in positions you would expect for a galaxy at that remote distance when you look at the predictions from our best lens models for this cluster,” Coe said. “We considered the full range of possibilities.”
NASA’s Spitzer Space Telescope played a key role in the team’s analysis by imaging the galaxy at longer wavelengths using the telescope’s Infrared Array Camera, or IRAC, which operates simultaneously on four wavelengths. If the MACS0647-JD galaxy were primarily red then it would appear bright in Spitzer’s images. The galaxy, however, was barely detectable to Spitzer, if at all, indicating its great distance. The research team plans to use Spitzer to conduct further observations of the galaxy, with the hopes of obtaining confident estimates of the galaxy’s age and dust content. MACS0647-JD may, however, simply be too far away for any current space telescope to confirm the distance based on spectroscopy, which disperses an object’s light into thousands of colors.
The discovery of the MACS0647-JD galaxy is the second “furthest object ever seen” uncovered in the CLASH survey. Earlier this year the team discovered another galaxy that existed when the universe was 490 million years old, 70 million years later than the new “distance champion” of MACS0647-JD.
The paper on the team’s study will appear in the December 20 issue of The Astrophysical Journal.