4,000,000,000,000, 000,000,000,000, 000,000,000,000, 000,000,000,000, 000,000,000,000, 000,000,000,000, 000,000,000,000
IN 13.7 BILLION YEARS, THAT’S HOW MUCH LIGHT IS THERE IN THE UNIVERSE
Let there light.
4 trillion trillion trillion trillion trillion trillion trillion particles of it, to be precise.
In one of those exercises that you think should be impossible or perhaps a punishment for some infraction, a team of astronomers has now measured the total amount of light that has ever been produced by all the stars in our universe.
The answer, expressed in terms of quantum particles of light known as photons, is 4 trillion trillion trillion trillion trillion trillion trillion. In scientific notation that is 4 x 10831/2, or, if you like, a 4 followed by 84 zeros. The big number
That number, reported in the journal Science by Marco
Ajello, an astrophysicist at Clemson University, and his colleagues, sounds big. But the universe is inconceivably vast, and in the grand cosmic scheme of things all of this light provides about as much illumination as a 60-watt bulb seen from 4-1/2km away. And the universe …
… is a bubble 14 billion light-years in radius. Astronomers estimate that the observable universe — which represents how far we have been able to see since its beginning — contains at least 2 trillion galaxies and 1 trillion trillion stars. Most of these stars and galaxies are too far and too faint to be seen with any telescope known to humans. But that doesn’t matter, Ajello and his colleagues say: All the energy ever radiated by these stars is still with us, filling the universe with a sort of fog, a sea of photons known as the extragalactic background light
(EBL). The (de) fault in our stars
Written in this starlight is the whole history of the birth and death of stars in the universe, from its beginning 13.7 billion years ago to its fraught present, which is why Ajello and his team wanted to measure it. They sought to dissect this fog and its history using data from the Fermi Gamma-ray Space
Telescope, a satellite that was launched in 2008 to study gamma rays, the most energetic form of electromagnetic radiation in the heavens. Among the oddities visible to this telescope are galaxies known as blazars, which are basically quasars, which are massive black holes that shoot out beams of high-energy gamma rays. Blazars are quasars whose high-energy beams happen to point right at Earth. Smashing the zero key …
… was not the only intention of the path-breaking study. Ryan F. Mandelbaum at Gizmodo reports that the measurement gives scientist an upper limit to the number of galaxies that were floating around
12 billion years ago during the
Epoch of Reionization, the period when dark matter, hydrogen and helium first coalesced into stars and ordinary matter. It’s also possible that the EBL measurement could help develop new ways to look for unknown particle types. The study also shows that the peak of star formation in the universe took place about 11 billion years ago. Over time, it has slowed drastically, but stars are still forming, with about seven new stars lighting up in the Milky Way every year alone. Exploding stars, dead dinosaurs and cosmic fog And how did the geniuses calculate it?
As gamma rays travel through space, they can collide with photons in the extragalactic background, producing pairs of electrons and losing a bit of energy in the process. Ajello and his team, using a decade worth of data collected by the Fermi telescope, measured the amount of gamma-ray energy thus lost from 739 blazars and one explosion known as a gamma-ray burst. The blazars ranged in distance from 200 million light-years to 11.6 billion light-years. Having calculated the energy lost to photon collisions across that distance (which, of course, is also time), the researchers could then determine the intensity of background light at various periods in cosmic history. They then could reconstruct the emergence of stars and galaxies starting about 1 billion years after the Big Bang. Rage against the dying of the light
If the starlight is dying, however, the universe as a whole might not notice enough to rage, to paraphrase the poet Dylan Thomas. Despite all those photons, starlight makes up only 1 millionth of the light in the universe, Ajello said. Far more photons were made in the Big Bang and now reside in the sky as the so-called cosmic microwaves. That is to say, 1,090 little packets of primordial energy, more or less.
Let there be light, indeed.
In the grand cosmic scheme of things all of this light provides about as much illumination as a 60-watt bulb seen from 4-1/2km away