Institute of Astronomy PUBLIC OPEN EVENING outreach — 3 October 2018 — A The galaxy collision that formed TONIGHT’S SPEAKER the Milky Way The talk schedule for this term can be viewed at: this term can be viewed talk schedule for The Matt Bothwell What on Earth is dark energy? Our weekly welcome ELCOME to our weekly public Wopen evenings for the 2018/19 season. Each night there will be a half-hour talk which begins promptly An impression of the collision between the Milky Way and the smaller Sausage galaxy about 8 at 7.15pm: tonight Matt Bothwell will to 10 billion years ago. Credit: V. Belokurov (Cambridge, UK) be giving us a talk entitled What on Earth is dark energy? AN INTERNATIONAL team of astron- Milky Way. However, the Sausage gal- The talk is followed by an oppor- omers has discovered an ancient and axy was much more massive: its total tunity to observe if (and only if!) the www.ast.cam.ac.uk/public/public_observing/current dramatic head-on collision between mass (including gas, stars and dark weather is clear. The IoA’s historical the Milky Way and a smaller object, matter) would have been more than Northumberland and Thorrowgood dubbed ‘the Sausage Galaxy’. The 10 billion times the mass of our Sun. cosmic crash reshaped the structure When it crashed into the young Milky telescopes, along with our modern of our Galaxy, fashioning both the Gal- Way, it caused a lot of mayhem. The 16-inch telescope, will be open axy’s inner bulge and its outer halo. Sausage’s piercing trajectory meant for observations. In addition, the The astronomers propose that that the Milky Way’s disk was probably Cambridge Astronomical Association around 8 to 10 billion years ago, an puffed up or even fractured following will provide a floorshow outdoors on unknown dwarf galaxy smashed into the impact, and the Milky Way had the Observatory lawns, relaying live our own Milky Way. The dwarf did not to re-grow a new disk. At the same images from their telescopes and survive the impact! It quickly fell apart, time, the Sausage debris was scat- providing a commentary. If we’re un- and the wreckage is now all around us. tered all around the inner parts of the lucky and it’s cloudy, we’ll offer you a “The paths of the stars from the Milky Way, creating the ‘bulge’ at the conciliatory cup of tea after the talk galactic merger earned the nickname Galaxy’s centre and the surrounding (with perhaps some more astro-in- ‘Gaia Sausage’” explained Wyn Evans ‘stellar halo’. formation in the lecture theatre for of the IoA. “We plotted the velocities The head-on collision of the of the stars, and the sausage shape Sausage galaxy was a defining event those who want to stay on). just jumped out at us. As the smaller in the early history of the Milky Way galaxy broke up, its stars were thrown that shaped our galaxy as we know it. out on very wide orbits. These Sausage Even though the merger took place in stars are what’s left of the last major the very remote past, the stars from If you have any questions, suggestions or merger of the Milky Way.” the Sausage galaxy can be picked out comments about the IoA Open Evenings There are ongoing mergers taking today. Evidence of this event lies all please contact Carolin Crawford at place right now, such as between the around us in the movements and com- [email protected] or Matt Bothwell at puny Sagittarius dwarf galaxy and the positions of stars. [email protected]. @cambridge_astro facebook.com/InstituteOfAstronomy 2 — IOA PUBLIC OPEN EVENING — 3 October 2018 having a simple ‘north magnetic pole’ like the Earth, Jupiter’s magnetic field Jupiter’s emerges from a large area spread across the whole northern hemisphere. And it magnetic has two – rather than one – magnetic ‘south poles’: one in the expected place field is even (at the South Pole!) and one just below weirder than the equator. Scientists are calling this newly-discovered magnetic pole the we thought ‘Great Blue Spot’. “Before the Juno mission, our best An illustration of maps of Jupiter’s field resembled Earth’s Jupiter’s magnetic field. field,” said lead author Kimberly Moore. Credit: NASA/JPL/SWRI “None of the existing models predicted a field like that.” These new findings indicate that MOST planets in the Solar System – start with, it’s amazingly strong: around something very strange must be going along with the Sun – have magnetic 20,000 times stronger than Earth’s. on inside Jupiter. One idea is that Jupi- fields, caused by processes going on Scientists have used this fact to try to ter’s magnetic field might be generated deep within their cores. Earth’s mag- understand Jupiter’s interior and came by a strange ‘slushy’ blend of liquid netic field is even surprisingly useful, up with a picture of a giant planet metallic hydrogen with ice and rock allowing compasses to point towards filled with ‘liquid metallic hydrogen’, chunks mixed in it. Another idea is magnetic north as well as protecting a strange substance produced when that ‘helium rain’ could be falling down us from harmful radiation. Planetary hydrogen is liquidised under unimagi- onto Jupiter’s core, knocking the field magnetic fields are caused by the so- nable pressures. off-kilter. called ‘dynamo effect’: deep oceans of A new study led by Kimberly Moore The Juno spacecraft will be making conducting fluids, rotating around the of Harvard University, using data from more observations of Jupiter in the planet cores. NASA’s Juno probe, has now revealed future, which scientists hope to use to We have long known that Jupiter’s that Jupiter’s magnetic field is even solve this mystery. magnetic field is surprisingly weird. To weirder than we thought. Rather than Shining out like a lighthouse through The brightest the fog, the authors say P352-15 ‘pre- sents the first real chance’ to study the ancient galaxy end of cosmic reionisation. The image above shows that P352-15 ever found. consists of three separate ‘blobs’. It is thought that one of these is the quasar THE quasar P352-15 may not look like itself, and the other two are powerful much, but it may be one of the useful ‘jets’, shot out of a supermassive black objects ever found for unlocking the hole at the quasar’s heart. mysteries of the early Universe. P352-15 will be an excellent can- After the Big Bang 13.7 billion years didate for more study with the ul- ago, the Universe rapidly settled down tra-powerful ‘Square Kilometre Array’, into the ‘dark ages’, with nothing but when the new radio telescope comes blackness until the first stars and The light in this image emanates from a supermassive black hole at the centre of a online in the 2020s. Astronomers hope galaxies formed and turned on the that learning more about P352-15 will lights. The effect of the first stars and galaxy 13 billion light-years away. Credit: Momjian, et al.; B. Saxton (NRAO/AUI/NSF) finally reveal better information about galaxies beginning to shine is known the processes involved in early galaxy as ‘reionisation’, and is one of the most formation, as well as giving us a better important processes for astronomers trying to get glimpses of the behaviour understanding of the growth of super- to understand. of the earliest galaxies. massive black holes. Trying to understand reionisation is That’s where quasars like P352-15 difficult though, because the Universe come in. P352-15 isn’t the most distant during the dark ages was very diffi- thing ever seen (that record goes to Joke of the Week cult to see through. For astronomers, a galaxy dubbed ‘GN-z11’) but it is studying the early Universe is a bit around 10 times brighter than any Why didn’t the sun go to college? like peering back through a misty veil, other galaxy seen at these distances. Because it already had 15 million degrees!.