Christmas Tree Galaxy Cluster Captured by NASA’s Hubble and Webb Team; What Do the Colors of the Images Mean?

NASA's Hubble Space Telescope and James Webb Space Telescope have combined forces to study an expansive galaxy cluster called MACS0416. They produced a stunning image considered one of the most comprehensive views of the universe ever taken.

Spotting a Stellar Giant

The panchromatic view of MACS0416 was created by combining infrared observations from JWST and visible-light data from Hubble. The image unveiled details that can only be captured by combining the power of both space telescopes.

The range of wavelengths from 0.4 to 5 microns resulted in a particularly vivid landscape of galaxies. To produce the image, blue color was assigned to the shortest wavelengths of light, red for the longest wavelengths, and green for the intermediate wavelengths.

The new Webb observations contribute to the aesthetic view but were taken for a specific scientific purpose. The research team combined three observations, each taken weeks apart, with a fourth epoch from the Canadian NIRISS Unbiased Cluster Survey research team. The researchers aim to search for objects, known as transients, which vary in observed brightness over time.

Fourteen transients were identified across the field of view, 12 of them located in three galaxies highly magnified by gravitational lensing. These are also likely to be individual stars or multiple-star systems that are magnified briefly. The remaining two transients are within more moderately magnified background galaxies and are assumed to be supernovae.

In particular, one transient captured the attention of astronomers. A star system was traced to a galaxy that existed 3 billion years after the creation of the universe from the Big Bang. It was nicknamed "Mothra," after the titular giant monster of a 1961 Japanese film, due to its extreme magnification and brightness.

Mothra has been previously detected by Hubble observations nine years ago. Astronomers were surprised at how this happened, suggesting that there must be a specific alignment between the galactic cluster and the more distant star, causing the magnification at a point in time.

How Mothra appeared magnified in the new Webb observations was likely due to a globular star cluster that is too faint for Webb to see directly, according to Institute of Physics of Cantabria researcher José Diego. As of now, they still do not fully understand the true nature of this additional lens.

Christmas Tree of Galaxies

MACS0416 is a pair of colliding galaxy clusters located about 4.3 billion light-years from Earth and is expected to combine to form an even bigger cluster. It is called Christmas Galaxy Cluster not only due to its color but also because of the flickering lights found within it.

The colors in the new image offer clues to galaxy distances. As best detected by Hubble, the bluest galaxies are relatively nearby and often indicate intense star formation, while the redder ones tend to be more distant, as Webb saw. Meanwhile, some galaxies appear very red because they contain abundant amounts of cosmic dust that absorb bluer colors of starlight.