The phrase "outer halo" refers to a faint glowing ring that surrounds the main bright part of something, like a person, object, or celestial body. It's like a gentle light that encompasses the outer edges, making the main thing stand out.
Sentences with «outer halo»
Spitzer's infrared view shows off the cooler outer halo of the dying star, colored here in red. (spitzer.caltech.edu)
Astronomers already had seen other large patterns of stars in our galaxy's vast outer halo, a sparsely populated sphere of old stars. (sciencemag.org)