An electron microscope image of a micron-sized supernova silicon carbide, SiC, stardust grain (lower right) extracted from a primitive meteorite. Such grains originated more than 4.6 billion years ago in the ashes of Type II supernovae, typified here (upper left) by a Hubble Space Telescope image of the Crab Nebula, the remnant of a supernova explosion in 1054. Laboratory analysis of such tiny dust grains provides unique information on these massive stellar explosions. (1 ?m is one millionth of a meter.) Credit: NASA and Larry Nittler.

Highlights • Non-classical MHC class I molecules promote homeostatic immunity to the microbiota • Commensal-specific T cells express immunoregulatory and tissue repair signatures • Commensal-specific T cells accelerate wound closure

This graphic shows the X-ray counterpart to the gravitational wave source GW170817, produced by the merger of two neutron stars. The left image is the sum of observations with NASA’s Chandra X-ray Observatory taken in late August and early Sept. 2017, and the right image is the sum of Chandra observations taken in early Dec. 2017. The X-ray counterpart to GW170817 is shown to the upper left of its host galaxy, NGC 4993, located about 130 million light years from Earth. The counterpart has become about four times brighter over three months. GW170817 was first observed on Aug. 17, 2017. Credit: NASA/CXC/McGill/J.Ruan et al.

Six years ago, Jiaxing Huang discovered crumpled graphene balls — novel ultrafine particles that resemble crumpled paper balls. Credit: Jiaxing Huang