JWST spots most distant barred spiral galaxy ever seen

An international team of astronomers has identified a massive barred spiral galaxy at a redshift of 5.1, making it the most distant such structure ever observed and pushing back the timeline for when organized galaxies could form after the Big Bang.

A Galaxy That Shouldn't Exist Yet

The galaxy, designated M1149-BSG-z5, was discovered using the James Webb Space Telescope in the parallel field of the galaxy cluster MACS J1149+2223. The findings, led by Xiaohan Wang of Tsinghua University in Beijing, were published on the preprint server arXiv on June 23.themoonlight+1

At a redshift of 5.102, M1149-BSG-z5 existed when the universe was roughly one billion years old — a period known as the Epoch of Reionization, when bar structure formation is expected to be suppressed by the turbulent cosmic environment. The galaxy hosts a stellar bar approximately 14,700 light-years long, spiral arms extending to about 17,900 light-years, and a stellar mass of roughly 28 billion solar masses.phys+2

Structural Maturity in a Young Universe

The discovery is notable because M1149-BSG-z5 exhibits features typically associated with far more evolved systems. Its star-formation rate was measured at about 144 solar masses per year, and spectroscopic analysis confirmed the presence of an active galactic nucleus with a broad-line component. The galaxy's metallicity — about 50 percent of the Sun's — indicates it is chemically mature, a trait not expected so early in cosmic history.themoonlight+1

Previous JWST observations had found barred galaxies emerging as early as a redshift of about 4.0, with observed fractions of just 3 to 7 percent at redshift 3.5. M1149-BSG-z5 extends this boundary further, and is larger than typical galaxies at comparable redshifts.phys+1

Clues to Bar Formation

The researchers noted that a companion galaxy lies approximately 69,000 light-years from M1149-BSG-z5, suggesting tidal interactions may have played a role in triggering bar formation. Alternatively, the galaxy's baryon-dominated, gas-rich state may have facilitated rapid bar development through gravitational instability, consistent with recent cosmological simulations.linkedin+2

The discovery adds to a growing body of JWST findings that suggest the early universe was more structured than previously thought. Before JWST, the earliest known barred galaxy was ceers-2112, dating back about 11.7 billion years. M1149-BSG-z5 pushes that record back by several hundred million years.nature