The first has to do with the small galaxies that are by far the most common in the Cosmos. California researchers announced, in the August 28 Nature, that they had discovered the minimum mass for those galaxies: It's 10 million times the mass of the sun. Why is this surprising, or even interesting? It's this: We'd always assumed that those cities of suns have no lower limit. Indeed, some galaxies are brighter and clearly contain more stars; others are smaller and dimmer. Over time, little galaxies merge to create larger ones, or else are pulled into already-existing major galaxies. Our own Milky Way cannibalized a small galaxy in just the past million years.
At least 22 dwarf galaxies orbit the Milky Way. Scientists, focusing on 18 of them in order to calculate their masses, determined how fast the individual stars were moving. Using those speeds, they found the weight of each galaxy.
Since dwarf galaxies vary so much in brightness - by a factor of 10,000 - we'd always believed that they had very different weights, with those with the most stars naturally possessing the heaviest mass. The bombshell is that all dwarf galaxies have the same mass.
In the article, one of the co-authors said, "Suppose you are an alien flying over Earth and identify urban areas from the concentration of lights in the night. From the brightness of the lights, [you'd surmise that more humans live in bigger, brighter cities than in small ones]." But this isn't what they found. "What we have discovered is more extreme - akin to saying that all metro areas, even those that are barely visible at night, have a population of 10 million."
Since dwarf galaxies, like all others, are mostly made of dark matter, the minimum-mass discovery reveals a fundamental property of this mysterious unseen entity. As the other study co-author explained, "We are excited because these galaxies are virtually invisible, yet contain a tremendous amount of dark matter." In short, this may teach us more about that invisible substance that makes up most of the material of the universe.
Our second discovery comes from British researchers summarizing and studying the brightest explosion ever seen, which was observed this past March 19.
Gamma Ray Bursts (GRBs) are brief, intense points of light that are observed about once a day, in totally random parts of the sky. Only some 15 years ago, astronomers realized that they come not from stars or unseen objects in our own galaxy, but solely in external galaxies: Nearly all are extremely distant.
In this recent, extraordinarily bright GRB, a jet from a powerful stellar explosion in a galaxy halfway across the universe was clearly aimed almost directly at Earth. It was bright enough to be seen by the naked eye. Fortunately, the Swift satellite, as it was designed to do, pinpointed this event almost the moment it occurred, and sent out an urgent bulletin to observatories around the world. Two robotic wide-field optical cameras in Chile also observed the flash, and within minutes many more telescopes were observing, setting up the most detailed study of a bright GRB ever undertaken - in visible, infrared, gamma-ray and radio wavelengths.
The astronomers present their findings in the September 10 issue of Nature. They conclude that the extraordinary brightness of the March 19 burst arose from a narrow jet that shot material directly towards Earth at 99.99995 percent of the speed of light. The data reveal that the narrow, ultrafast jet exists within a wider, slightly slower jet, so that the faster one caught up with the previous one.
Obviously, as we'd suspected for some time, the amazing energy released by the apparent collapse of a massive star's core to form a black hole doesn't radiate in all directions. If it did, then the tiny slice of power that we perceive here, extrapolated to the total energy that must be emitted, could have no possible explanation within the realm of science. Nothing can create that much power.
Instead, the inner jet - so narrow that a hundred of them would need to be lined up to mark off the width of the moon - had to be pointing at the Earth, aimed our way by unimaginably powerful magnetic fields. (The daily, run-of-the-mill GRBs instead produce a much wider - and hence far less luminous shaft of energy - also beamed our way). The type that just went kaplooie a few months ago probably only happens once per decade or so.
In case you wonder why anything should be beamed our way...well, apparently these violent events occur throughout the Cosmos, aimed randomly. We only see the tiny fraction that happens to be aligned in our direction. Said one of the researchers, "On March 19, we got lucky."
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