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Cosmic Questions

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My son, Finn, loves asking questions.

When he was about five, he discovered that I was an astronomer. He quickly realized that there was now an entire universe of questions he could direct my way, confident that his clever dad would have all the answers. And with my Ph.D. in astrophysics and many years of subsequent research and teaching under my belt, I was equally confident I could handle the questions he'd throw at me.

"What's the coldest place in outer space? How fast can stars move? Where is the strongest gravity in the universe? And what about the strongest magnet?"

Simple enough questions, but to my surprise and embarrassment, these were questions I wasn't able to immediately answer. As a professional astronomer, I can explain in detail to my students how stars shine, how planets orbit, or how we measure the distance to the farthest galaxies. But these aren't the answers that five-year-olds care about. Five-year-olds only want to know about the biggest, the baddest, and the most extreme. In contrast, the "world records" of the cosmos simply aren't important things for an astronomer to know or think about.

Desperate not to appear diminished in my son's eyes, I set out find answers to his questions. Inevitably, my first step was Google and Wikipedia, but I quickly found either that the results were over-simplified and out-of-date, or that the answers simply weren't out there at all. But I was a scientist, and I had the entire vast literature of astrophysical research at my disposal. I started with a list of my son's ten most pressing questions about the universe, and I got to work.

To find the answers, I had to read more than 300 journal articles, most in topics well outside my area of expertise. In some cases I couldn't find anything at all on the questions that I was trying to address, so I had to calculate the answers myself. Two years later I was done, and I could finally give my eager son the answers he had been demanding.

The coldest known place in space? Turns out the answer is an icy cloud of gas called the Boomerang Nebula, which has a bone-chilling temperature of -458°F. This is less than two degrees above "Absolute Zero," the coldest temperature allowed by the laws of physics.

The fastest-moving star? That record goes to a star with the catchy name "PSR B2224+65", which moves through space at an incredible 3.6 million miles per hour. It's hard to imagine how fast this is: 4,700 times the speed of sound, and 50 times faster than the orbit of the Earth around the Sun. PSR B2224+65 travels the distance from Los Angeles to New York every 2.5 seconds, and the distance from the Earth to the Moon every four minutes.

The strongest gravity? A black hole known as "GRO J0422+32", whose gravitational pull is 400 billion times stronger than the Earth's. If you somehow managed to drop a stone into this black hole from a vantage point of 30 feet above it, the stone would take just two-millionths of a second to drop, and would fall into the black hole at a speed of 6000 million miles per second.

And the strongest magnet? A star called "SGR 1806-20", whose magnetic field is 10 trillion times stronger than a fridge magnet. The magnetism of SGR 1806-20 is so intense that even if SGR 1806-20 were 600,000 miles away (almost three times the distance to the Moon), its magnetism would overwhelm that of the Earth, making compass navigation impossible. At a distance of 60,000 miles, it would wipe the data from every credit card and hard drive on the planet. And at 10,000 miles, the magnetic field of SGR 1806-20 would be fatal, because it would now be so intense that it would disrupt the electrical nerve impulses that make your heart beat. Fortunately, SGR 1806-20 is more than 30,000 light-years away, and so does not produce these effects!

These and other answers taught me that the universe was even more amazing then I imagined, and I also discovered that the journey was just as thrilling as the final answers. So after I had satisfied, at least temporarily, my son's inquires, I decided to share these stories more widely, and to color the journey with some of the details and sophistication that are perhaps beyond a young boy's attention span. The result is the book Extreme Cosmos, my attempt at a definitive compendium of the records of the cosmos: the coldest, the fastest, the biggest, the brightest, and even the loudest.

If there's a unifying conclusion I've been able to draw from the extraordinary objects I've written about, it's an appreciation of what a small and marginal role we play in the universe. Our entire Milky Way galaxy is an unimportant, minute fleck on the celestial stage, an irrelevant region of bright light and dense gas, hidden amid the vast darkness and emptiness of much larger cosmic voids. On the other hand, what a triumph of pure thought it has been, that we mere humans, in the space of little more than a hundred years, have established how stars are born, live and die, how galaxies evolve, and how the whole vast ensemble of stars, gas and galaxies fit together.

The cosmos is unquestionably extreme, and the numbers that measure these extremities can at first seem hard to comprehend. However, on closer inspection, the universe's extremes become not only comprehensible, but turn out to be the vital keys needed to unlock the true wonder and elegance of the heavens. Despite the seemingly hopeless mismatch between our limited, human, imaginations and the size and complexity of the universe, it's astonishing that we can understand so much of what we see. As baffled and cowed as we often find ourselves when confronted by the cosmos, it is perhaps humanity's ultimate accomplishment that we nevertheless can explain and appreciate the grandeur of the night sky.

Bryan Gaensler is the author of Extreme Cosmos.