gravity
esiegel | October 28, 2016“All enterprises that are entered into with indiscreet zeal may be pursued with great vigor at first, but are sure to collapse in the end.” -Tacitus
Dark matter makes up the overwhelming majority of mass in the Universe. With five times as much of it as there is normal matter, and the fact that it doesn’t emit or absorb light but does interact gravitationally, it might seem like the perfect candidate to form black holes. After all, it’s named “dark matter” to begin with, and black holes are perhaps the darkest form of matter in the whole Universe.
While stars might cluster in the disk and…
esiegel | September 19, 2016“It may be that ultimately the search for dark matter will turn out to be the most expensive and largest null result experiment since the Michelson-Morley experiment, which failed to detect the ether.” -John Moffat
Dark matter is a puzzle that’s now more than 80 years old: the presence of all the known, observable, detectable normal matter — the stuff in the standard model — cannot account for the gravitation of the astronomical objects we observe. But despite our inability to create or detect it in a laboratory, we’re certain of its existence in the Universe.
Numerical simulation of the…
esiegel | September 10, 2016“Mapping out the elements in a star is like reading its DNA. We’re using those DNA readings to decode the history of the Milky Way from the stars that we can observe today.” -Steven Majewski
Most of the stars in our Milky Way have long lives ahead of them, with dozens or even hundreds of orbits around the entire galaxy to come over their lifetimes. With hundreds of billions of stars involved in this cosmic dance, it stands to reason that on occasion, another nearby star will either gravitationally or cataclysmically (e.g., from a supernova) kick such a star to incredible velocities, perhaps…
esiegel | August 23, 2016“Astronomers are greatly disappointed when, having traveled halfway around the world to see an eclipse, clouds prevent a sight of it; and yet a sense of relief accompanies the disappointment.” -Simon Newcomb
Next year, on August 21st, 2017, millions of Americans will delight in the first total solar eclipse to go from coast-to-coast in 99 years. The path of totality will range from Oregon to South Carolina, giving more than two minutes of the Sun being blocked by the Moon’s shadow to all along its central path.
Image credit: Mir / RSA, 1999, of the Moon's shadow falling on Earth, during a…
esiegel | July 26, 2016"Dimension regulated the general scale of the work, so that the parts may all tell and be effective." -Vitruvius
In a four-dimensional Universe (3 space and 1 time), it’s easy to get lost. If you take a random walk, the chances of you coming back to your original starting point in a finite number of steps gets lower and lower the more dimensions you have. If all you could do was walk along a sheet of paper -- or even better, along the surface of a pipe -- you’d have a much greater chance of return than if you had all three spatial dimensions to deal with.
Isotropic random walk on the…
esiegel | July 23, 2016"We detect motion along this axis, but right now our data cannot state as strongly as we'd like whether the clusters are coming or going." -Alexander Kashlinsky
When dark energy was discovered, and the expansion of the Universe was shown to be accelerating, there was concurrently another puzzle that received much less attention: the problem of the Great Attractor. Galaxies appear to move due to both the Hubble expansion and the local gravitational field, but the gravity from the galaxies we saw didn’t account for all the motion.
The "flows" of galaxies mapped out with the mass field nearby.…
esiegel | June 30, 2016"How well I have learned that there is no fence to sit on between heaven and hell. There is a deep, wide gulf, a chasm, and in that chasm is no place for any man." -Johnny Cash
The largest mountains, the greatest chasms, steepest cliffs and the tallest peaks on Earth are certainly impressive, particularly when compared to the scale of a human. But compared to the mountains on Mars, Io, Vesta or Iapetus, or the canyons and cliffs on Mars, Mercury, or even Charon, Earth’s features look puny.
Valles Marineris on Mars, taken by the Viking orbiters. Image credit: NASA.
How could these small…
esiegel | June 25, 2016"You can be the Moon and still be jealous of the stars." -Gary Allen
Earlier this week, NASA announced the discovery of Asteroid 2016 HO3, calling it Earth’s second moon. And it turns out that this is an object in a stable orbit, the same distance from the Sun as the Earth, that can be found revolving around our world at a distance between 38 and 100 times the distance from us to the Moon.
The orbits of all the known Potentially Hazardous Asteroids, as of 2013. This includes asteroids that have been gravitationally captured by the Earth-Sun system. Image credit: NASA/JPL-Caltech.
But that…
esiegel | June 22, 2016"We shall not cease from exploration, and the end of all our exploring will be to arrive where we started and know the place for the first time." -T.S. Eliot
Now that not just one but two gravitational wave events have been directly detected, we're officially in the era of true gravitational wave astronomy. LIGO has taught us something unique about stellar mass black holes, and will continue to teach us about these objects, their population statistics, and their merger rates as time goes on.
Image credit: Bohn et al 2015, SXS team, of two merging black holes and how they alter the appearance…
esiegel | June 15, 2016"It turned out that nature was very kind, and there appear to be many of these black holes in the Universe and we were lucky enough to see one." -Dave Reitze, executive director of LIGO
On September 14th, 2015, just days after turning on, the twin Advanced LIGO detectors detected the first gravitational wave signature: a merger between two black holes, of 36 and 29 solar masses. They inspiraled, they merged, and they lost 5% of their rest mass to gravitational radiation, sending ripples through the fabric of space due to Einstein’s E = mc^2. It raised a whole slew of questions: were these…
esiegel | May 23, 2016"The first amazing fact about gravitation is that the ratio of inertial mass to gravitational mass is constant wherever we have checked it. The second amazing thing about gravitation is how weak it is." -Richard Feynman
One of the strangest, most novel predictions of Einstein's relativity is that mass would not only curve space, but that the curved space would act like a lens. Background light traveling past this mass would become magnified, distorted and stretched. In some cases, arc, multiple images or even perfect, 360º rings would occur.
This image illustrates a gravitational lensing…
esiegel | May 20, 2016"To explain all nature is too difficult a task for any one man or even for any one age. 'Tis much better to do a little with certainty & leave the rest for others that come after you." -Isaac Newton
Perhaps the greatest, most successful scientific theory of the past century is Einstein's General Relativity, our theory of gravitation that has answered every challenge to it for the past 101 years with resounding success. Yet before that, Newton's gravity did the same thing for more than twice as long! The culprit that finally brought the universal theory of ground was incredible in its…
esiegel | May 12, 2016“Even if I stumble on to the absolute truth of any aspect of the universe, I will not realise my luck and instead will spend my life trying to find flaws in this understanding – such is the role of a scientist.” -Brian Schmidt
Imagine you had arbitrarily great technology, limitless energy, and the ability to accelerate as close to the speed of light for as long as you wanted. Would you be able to reach the most distant galaxies, the leftover glow from the Big Bang or anything beyond the limit of what we can see today?
Image credit: NASA, ESA, and Z. Levay (STScI). The GOODS-North survey,…
esiegel | April 28, 2016"The fact that gravitational damping is measured at all is a strong indication that the propagation speed of gravity is not infinite. If the calculational framework of general relativity is accepted, the damping can be used to calculate the speed, and the actual measurement confirms that the speed of gravity is equal to the speed of light to within 1%." -Steve Carlip
According to General Relativity, the speed of gravity must be equal to the speed of light. Since gravitational radiation is massless, it therefore must propagate at c, or the speed of light in a vacuum. But given that the Earth…
esiegel | April 26, 2016"The world is the great gymnasium where we come to make ourselves strong." -Swami Vivekananda
But what does it truly mean to be strong? We have four fundamental forces in the Universe: the strong, electromagnetic, weak and gravitational forces. You might think that, by virtue of its name, the strong force is the strongest one. And you'd be right, from a particular point of view: at the smallest distance scales, 10^-16 meters and below, no other force can overpower it.
Image credit: Sloan Digital Sky Survey, of IC 1101, the largest known individual galaxy in the Universe.
But under the…
esiegel | April 7, 2016"All truths are easy to understand once they are discovered; the point is to discover them." -Galileo Galilei
Galileo is most famous for his astronomical discoveries, including the moons of Jupiter, the existence of sunspots and the phases of Venus. These discoveries were a strong challenge to geocentrism, and his writings and debates helped popularize the heliocentric model.
Image credit: Wikimedia Commons user Fernando de Gorocica, under a c.c.a.-s.a.-3.0 license, of Galileo’s original (1610) sketches of the phases of Venus.
Yet, in a recent article for Aeon magazine, Thony Christie…
esiegel | April 6, 2016"I'm here for several reason, Mr. Pepin, first of all for aid. When something tragic happens in our skies, we do our utmost to extend sympathy. But sympathy without action,that's an empty emotion. Mainly I'm here for the purposes of reentry."
"I don't understand."
"Adjustment," Harold said, "to earth. I'm here to make sure you didn't leave your whole life in the sky." -Adam Ross
When we launch a satellite into orbit around the Earth, we expend a tremendous amount of fuel and energy to make it happen. From hundreds of miles up -- well above the definition of space -- these satellites zip…
esiegel | March 10, 2016"If you are not completely confused by quantum mechanics, you do not understand it." -John Wheeler
Now that LIGO has detected gravitational waves directly, it's time to examine all the different sources that they come from, and what they can teach us about the Universe. While accelerating masses in strong gravitational fields -- black holes, neutron stars and the like -- will produce gravitational waves capable of being seen by direct detection experiments, there's another class of gravitational waves that's observable through its effects on the leftover light from the Big Bang: gravitational…
esiegel | February 20, 2016“You asked me how to get out of the finite dimensions when I feel like it. I certainly don't use logic when I do it. Logic's the first thing you have to get rid of.” -J.D. Salinger
Now that gravitational waves have been verified to exist, and the first black hole-black hole merger has been definitively detected by LIGO, it's time to start thinking of the next steps in gravitational wave astronomy. The biggest one we can dream of, perhaps the holy grail of this field of study, is to go beyond General Relativity itself, and to find evidence that gravitation is a truly quantum theory at its core…
esiegel | February 17, 2016“If the imprint is really due to gravitational waves from the big bang, then this is the type of cosmological discovery that comes along perhaps once every fifty years.” -Kip Thorne
Now that LIGO's successfully detected it's first gravitational waves — from two merging black holes — we know that we will find them in a variety of circumstances if we look in the right way.
Illustration of a fast gamma-ray burst, previously only thought to occur from the merger of neutron stars. Image credit: ESO.
While LIGO and its successors will be great for exploring high-frequency events like small black…