shell structures (IMAGE) Rensselaer Polytechnic Institute Caption Stars identified in the research have formed "shell structures" in the aftermath of a radial merger occurring 3-billion years ago. Credit Rensselaer Polytechnic Institute Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.