Universe – The Milky Way: Island of Light episode 3: Professor Brian Cox continues his epic exploration of the cosmos by exploring the faint band of light that sweeps across the night sky – our own galaxy, the Milky Way. The Sun is just one of almost 400 billion stars that form this vast, majestic disk of light, our own home in the universe. We’ve longed to understand our galaxy’s secrets since the time of the ancient Greeks, yet it’s only very recently, thanks to a cutting edge space telescope, that we’re finally able to reveal the Milky Way’s dramatic history and predict its cataclysmic future.
One mission more than any other has deepened our understanding of the galaxy, the European Space Agency’s Gaia Space Telescope. It painstakingly measures the true position of over a billion stars, producing the most accurate map of our galaxy ever created. But more than mapping stars, Gaia also measures their movement, allowing us to track their positions back through time – to rewind the history of the Milky Way. It has created a new kind of science: galactic archaeology.
Our galaxy started to form shortly after the Big Bang around 13.6 billion years ago. It started out a fraction of the size it is today, and Gaia has revealed how it grew over the eons. Beautifully rendered VFX based on the very latest Gaia data has uncovered the remarkable story of our galaxy’s evolution as it grew through a series of violent growth spurts and intense periods of cataclysmic change, as our young galaxy encountered rival galaxies while battling to survive.
Over billions of years, our Milky Way cannibalised neighbouring galaxies, adding countless new stars and triggering great epochs of creation. Brian reveals we may even owe our own existence to one of these galactic collisions. Each time our galaxy feeds, a new era of star formation begins, fuelled by incoming torrents of fresh gas and energy. The latest evidence suggests that our own star was possibly born in one such event.
We may be small compared to the universe, but we are the consequence of grand events, and there is another collision to come. Another, larger galaxy is coming our way. Andromeda is heading straight for us at a quarter of a million miles per hour. The Milky Way’s long-term fate is in the balance.
Universe – The Milky Way: Island of Light episode 3
The Milky Way is the galaxy that includes the Solar System, with the name describing the galaxy’s appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλακτικός κύκλος (galaktikos kýklos), meaning “milky circle.” From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.
The Milky Way is a barred spiral galaxy with an estimated visible diameter of 100,000–200,000 light-years. Recent simulations suggest that a dark matter disk, also containing some visible stars, may extend up to a diameter of almost 2 million light-years. The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster, which is itself a component of the Laniakea Supercluster.
It is estimated to contain 100–400 billion stars and at least that number of planets. The Solar System is located at a radius of about 27,000 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust. The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The galactic center is an intense radio source known as Sagittarius A*, a supermassive black hole of 4.100 (± 0.034) million solar masses.
Stars and gases at a wide range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant rotational speed appears to contradict the laws of Keplerian dynamics and suggests that much (about 90%) of the mass of the Milky Way is invisible to telescopes, neither emitting nor absorbing electromagnetic radiation. This conjectural mass has been termed “dark matter”. The rotational period is about 240 million years at the radius of the Sun. The Milky Way as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference. The oldest stars in the Milky Way are nearly as old as the Universe itself and thus probably formed shortly after the Dark Ages of the Big Bang.
