Einstein Cross Reveals Mystery of Young Galaxies With Old Stars

Astronomers have identified a rare Einstein Cross gravitational lens that reveals a young elliptical galaxy containing surprisingly mature stars. The discovery of the galaxy, designated as J1453g, provides new data on how galaxies formed and evolved in the early universe.

The galaxy J1453g is observed as it existed approximately 8 billion years ago, a time when the universe was less than 6 billion years old. Despite being a primordial galaxy in its early stages of development, researchers found that J1453g is surprisingly similar to the Milky Way.

This finding suggests that the growth and evolution of galaxies may be more complex than previous scientific theories had proposed. J1453g represents the first gravitational lens at a large cosmic distance that astronomers have been able to precisely weigh.

The Mechanics of the Einstein Cross

An Einstein Cross occurs through gravitational lensing, a phenomenon where massive objects bend spacetime according to the general theory of relativity. When a massive object like a galaxy aligns precisely with a more distant light source, it bends the light from that source.

In the case of J1453g, the galaxy lenses the light from a more distant quasar, which is a region of space dominated by a supermassive black hole. This alignment magnifies the light and causes the quasar to appear as four distinct images arranged symmetrically around the lensing galaxy in the shape of a cross.

These alignments are considered exceedingly uncommon because they require precise positioning along the line of sight. Only a small number of such systems have been documented since the first Einstein Cross quasar system was identified in 1985.

Insights Into Early Galaxy Assembly

Elliptical galaxies are typically characterized by smooth, featureless shapes. They are generally dominated by older, redder stars and exhibit very little ongoing star formation.

The presence of such a galaxy so early in the history of the universe raises questions regarding the rapid assembly processes that occurred shortly after the Big Bang. The magnification provided by the Einstein Cross allows for detailed spectroscopy that would otherwise be impossible.

Researchers utilized ground-based observatories as well as telescopes such as ALMA and Hubble to detect the system. The gravitational lensing can boost the brightness of the remote object by factors of tens or more, exposing fine details in the spectra.

The discovery of this exceptional object has allowed us to accurately study the nature of the stars at the center of an elliptical galaxy in a remote era of the universe, when the galaxy was still young

Quirino D’Amato, researcher at the Italian National Institute for Astrophysics (INAF)

Scientific Implications

The observation of mature stars within a young galaxy challenges existing assumptions about how stellar populations are assembled over cosmic time. It indicates that some galaxies may have reached a state of maturity much faster than previously expected.

By studying J1453g, the team led by D’Amato can better understand the nature of stars at the center of elliptical galaxies during remote eras of the universe. This provides a window into the conditions of the cosmos during its infancy.