Interstellar Mile Markers

Interstellar Mile Markers

Physics professor Glenn Starkman, PhD, and colleagues from two institutes have devised a technique to use the light emitted by quasars—quasi-stellar radio sources—as a yardstick to measure how the universe has grown.

Not stars but rather black holes glowing as they swallow their surroundings, quasars are some of the brightest and most distant objects in the universe. Starkman’s technique, when combined with the expected discovery of millions more faraway quasars over the next decade, could yield an unprecedented look back to a time shortly after the Big Bang.

The findings were published last year in Physical Review Letters.

In a study of 14 quasars, researchers found patterns of light variation over time were consistent from one quasar to another when corrected for what’s known as the quasar’s redshift. The redshift occurs because as the universe expands, it carries the quasars away from us, shifting quasar light toward the red end of the spectrum.

By turning this process around, researchers could compare the light variations they observed and the standard rate at which the light from quasars sampled actually vary. That information allowed them to infer the redshift of the quasar.

Knowing the quasar redshift enables the scientists to calculate the relative size of the universe when the light was emitted. If the technique proves true, the most distant quasars emitted the light we see now back when the universe was one-eighth the size it is today. Older, more distant quasars that are expected to be discovered with new telescopes could provide looks farther into the past.