Free Astronomy Magazine July-August 2020

53 JULY-AUGUST 2020 SPACE CHRONICLES ALMA we now have unambiguous evidence that they occur as early as 1.5 billion years after the Big Bang,” said lead author Marcel Neeleman of the Max Planck Institute for As- tronomy in Heidelberg, Germany. The discovery of the Wolfe Disk pro- vides a challenge for many galaxy formation simulations, which pre- dict that massive galaxies at this point in the evolution of the cosmos grew through many mergers of smaller galaxies and hot clumps of gas. “Most galaxies that we find early in the Universe look like train wrecks because they underwent consistent and often ‘violent’ merg- ing,” explained Neeleman. “These hot mergers make it difficult to form well-ordered, cold rotating disks like we observe in our present Universe.” In most galaxy formation scenarios, galaxies only start to show a well- formed disk around 6 billion years after the Big Bang. The fact that the astronomers found such a disk galaxy when the Universe was only ten percent of its current age, indi- cates that other growth processes must have dominated. “We think the Wolfe Disk has grown primarily through the steady accretion of cold gas,” said J. Xavier Prochaska, of the University of Cali- fornia, Santa Cruz and coauthor of the paper. “Still, one of the ques- tions that remains is how to assem- ble such a large gas mass while maintaining a relatively stable, ro- tating disk.” A rtist impression of the Wolfe Disk, a massive rotating disk galaxy in the early, dusty Universe. The galaxy was initially discovered when ALMA examined the light from a more distant quasar (top left). [NRAO/AUI/NSF, S. Dagnello]