'Cepheids follow a relation between their pulsation period and luminosity, allowing the intrinsic luminosity
of a Cepheid to be inferred from its period.
As there is a relationship between the period of the star's oscillations and its luminosity, one can infer the intrinsic luminosity
and compute the distance.
But its intrinsic luminosity
was twice as bright as any supernova yet discovered.
Objects such as these, termed standard candles because they could be thought of as light sources whose luminosities were very well regulated, were a valuable tool for estimating the distances of astronomical objects because their observed brightnesses could be thought of as depending purely upon their distance, rather than any variability in their intrinsic luminosity
. Faint standard candles were a long way away, and bright standard candles were nearby.
Previous studies have suggested that this type, known as a supernova la, has the same intrinsic luminosity
in both nearby and distant galaxies.
Having run out of hydrogen to fuse in their cores, they struggle to burn shells of helium instead, puffing up and deflating at a rate directly tied to their intrinsic luminosity
The faintness of this low-mass star, which has only about one-fortieth the intrinsic luminosity
of the sun, made it difficult to analyze.
I had been waiting for the perfect night to attempt these massive young stars, whose intrinsic luminosity
is 250,000 times that of the Sun!
Because these supernovas have roughly the same intrinsic luminosity
, their apparent brightness indicates their distance from Earth.
What makes Cepheids so special is that they exhibit a distinct relationship between their period and their intrinsic luminosity
. By measuring a Cepheid's cycle time, which can range from less than a day to more than two months, astronomers gain an excellent indication of how far away it is.
Matching the inferred rate of star formation to both the rate and spectra of observed gamma-ray bursts, and assuming that gamma-ray bursts all have about the same intrinsic luminosity
, Ralph A.M.J.