S27E63: Galactic Archaeology: Unearthing the Milky Way's Earliest Star Clusters

[00:00:00] This is SpaceTime Series 27 Episode 63 for broadcast on the 24th of May 2024.

[00:00:07] Coming up on SpaceTime, some of the universe's oldest stars found in our own celestial backyard,

[00:00:13] Europe's due spacecraft now a year into its eight-year journey to Jupiter, and

[00:00:18] Russia test launches its new heavy-lift Angara A5 rocket. All that and more coming up on SpaceTime.

[00:00:27] Welcome to SpaceTime with Stuart Gary.

[00:00:46] Astronomers have discovered three of the oldest stars in the universe

[00:00:50] in the halo of our own Milky Way galaxy. The galactic halo is the cloud of stars that

[00:00:56] envelops the entire main galactic disk. The new findings reported in the journal

[00:01:01] The Monthly Notices of the Royal Astronomical Society suggest that these three newly discovered

[00:01:05] stars formed somewhere between 12 and 13 billion years ago.

[00:01:10] Now that's a time when some of the very first galaxies were only starting to take shape.

[00:01:15] The researchers have coined the stars SAS, which stands for Small Accreted Stellar System Stars.

[00:01:21] That's because they believe each star once belonged to its own small primitive galaxy

[00:01:25] that was later absorbed by the larger but still growing Milky Way. Today it seems these three

[00:01:31] stars are all that's left of their respective galaxies. The study's lead author Anna Frebel

[00:01:37] says there are likely to be lots of similar ancient stars in the galactic halo, given what

[00:01:41] astronomers already know about galaxy formation. As they uncover similar SAS stars, the authors

[00:01:47] hope to use them as analogues of ultra-faint dwarf galaxies, which are thought to be some

[00:01:51] of the universe's surviving first galaxies. Such galaxies are still intact today, but they're too

[00:01:57] distant and too faint for astronomers to study them in depth. So, as SAS stars may have once

[00:02:03] belonged to similarly primitive dwarf galaxies but are in the Milky Way and therefore much closer,

[00:02:08] they could be an accessible key to understanding the evolution of ultra-faint dwarf galaxies.

[00:02:13] Frebel says the team can now go looking for more analogues in the Milky Way where they're much

[00:02:17] brighter and easier to find and study their chemical evolution without having to chase these

[00:02:22] extremely faint stars. The group collected star data collected by Frebel using the 6.5-meter

[00:02:28] Magellan Clay Telescope at the Los Campos Observatory in Chile. They were searching

[00:02:33] for ancient stars that would have formed soon after the Big Bang 13.8 billion years ago.

[00:02:38] During this time, the universe was made mostly of hydrogen and helium,

[00:02:43] and very low abundances of other chemical elements such as strontium and barium.

[00:02:47] So, the team looked through Frebel's catalogue of stars with spectra,

[00:02:51] that is measurements of light coming from stars that provide clues about the chemical composition.

[00:02:56] And they were especially looking for low abundances of strontium and barium.

[00:03:01] Eventually their search narrowed down to three stars originally observed by Magellan in 2013

[00:03:05] and 2014. It seems the original observations were never followed up to interpret their spectra and

[00:03:11] deduce their origins. So, the authors undertook the work finding that these three target stars

[00:03:16] had very low abundances of strontium and barium as well as other elements such as iron when

[00:03:21] compared to a reference star, in this case the Sun. In fact, one star contained less than 1

[00:03:26] ten-thousandth the amount of iron to helium compared to the Sun today. Now, the low chemical

[00:03:31] abundance in these stars indicated that their ages are likely to be between 12 and 13 billion

[00:03:37] years old. In fact, their low chemical signatures were similar to what astronomers had previously

[00:03:42] measured in some ancient ultra-faint dwarf galaxies. So, the authors then checked the

[00:03:47] stars' proper motion across the sky, that is their orbital trajectories. The three stars are each in

[00:03:53] different locations in the galactic halo and each are estimated to be about 30,000 light years from

[00:03:58] Earth. Overall, the Milky Way's disk spans some 100,000 light years in diameter and we're roughly

[00:04:04] 27,000 light years from the galactic center. So, these stars are a long way out. Now, as they

[00:04:10] traced each star's path around the galactic center using observations from the European Space

[00:04:14] Agency's Gaia satellite, they noticed that all three stars seemed to be going in the wrong way,

[00:04:19] that is in retrograde motion compared to most of the other stars in the Milky Way.

[00:04:23] And that suggests that each of them must have originated in another galaxy which was cannibalized

[00:04:28] by the Milky Way billions of years ago. The authors have now found some 65 additional stars also with

[00:04:34] low strontium and barium abundances. And they also appear to be orbiting in retrograde,

[00:04:39] suggesting once again that they're all ancient and belong to other smaller dwarf galaxies that

[00:04:44] fell into the Milky Way at random angles with the stars continuing on strange trajectories billions

[00:04:49] of years later. This is Space Time. Still to come, the European Space Agency's JUICE spacecraft,

[00:04:57] now a year into its eight-year journey to Jupiter, and the Kremlin undertakes a successful test launch

[00:05:03] of Russia's new heavy-lift Angara A5 rocket. All that and more still to come on Space Time.

[00:05:25] The Jupiter Icy Moons Explorer, or JUICE spacecraft, has just celebrated its first year in

[00:05:30] space as it continues its epic eight-year journey to the Jovian ice moons Ganymede, Callisto and

[00:05:37] Europa. Launched aboard an Ariane 5 rocket from the European Space Agency's Kourouc

[00:05:42] spaceport in French Guiana back on April 14 last year, the interplanetary probe is targeting the

[00:05:47] three Galilean moons because they're all thought to have significant bodies of liquid water beneath

[00:05:52] their frozen surfaces. And that makes them each a potential habitable environment for extraterrestrial

[00:05:59] life. JUICE is the only interplanetary spacecraft to the outer solar system's planets not launched

[00:06:05] by the United States, and it will be the first to orbit a set of moons other than Earth's.

[00:06:11] There are four gravity assists planned by JUICE in order to place it on a trajectory to reach

[00:06:16] Jupiter. Firstly, there will be a flyby of the Earth-Moon system in August this year. That'll

[00:06:21] be followed by a slingshot around Venus in August next year, a second flyby of the Earth in September

[00:06:26] 2026, and a third and final flyby of the Earth in January 2029. JUICE will pass through the

[00:06:33] asteroid belt twice on its way to the Jovian system. A flyby of the asteroid 223 Rosa was

[00:06:39] proposed to occur in October 2029, but it was abandoned to save fuel for the primary mission.

[00:06:45] Finally, in April 2031, JUICE will fly by Jupiter's moon Callisto, offering scientists a

[00:06:51] tantalizing glimpse at this mysterious cratered alien world. It's expected to achieve Jovian

[00:06:57] orbit insertion in July, and in December 2034, the spacecraft will finally enter orbit around

[00:07:02] Ganymede for its close-up science mission. JUICE will perform a detailed investigation of Ganymede

[00:07:08] and evaluate its potential to support life. The mission will characterize the giant moon's

[00:07:13] subsurface ocean and water reserves. It will undertake a topographical, geological, and

[00:07:18] compositional mapping survey of its surface, including the physical properties of its icy

[00:07:23] crust. JUICE will also characterize Ganymede's internal mass distribution, its dynamics,

[00:07:28] and evolution of its interiors. It will study the moon's tenuous atmosphere, as well as its

[00:07:34] intrinsic magnetic field and the field's interaction with the Jovian magnetosphere.

[00:07:39] Investigations of Europa and Callisto will complete a comparative picture of these three

[00:07:44] Galilean moons. For Europa, the focus will be on the chemistry essential for life, including organic

[00:07:49] molecules, and on understanding the formation of surface features and the composition of the

[00:07:54] non-water-ice material. JUICE will also provide the first subsurface sounding of the moon,

[00:07:59] including the first determination of the minimal thickness of the icy crust over the most

[00:08:03] recently cryovolcanically active regions. More distant spatially resolved observations will also

[00:08:09] be carried out for several minor irregular satellites, as well as the volcanically active

[00:08:14] moon of Io. This report from ESA TV. The giant planet Jupiter is a place of intrigue and mystery.

[00:08:24] A special environment within our own solar system. When Galileo first raised his telescope to the

[00:08:31] planet, he discovered four moons, Io, Europa, Ganymede, and Callisto. Early space probes

[00:08:40] raised more questions than answers about this fascinating gas giant planet and its intriguing

[00:08:46] moons. Now, those answers are within our grasp. The Jupiter Icy Moons Explorer, JUICE.

[00:08:55] JUICE is equipped with the most powerful science payload ever sent to the outer solar system.

[00:09:02] Ten instruments will conduct the most comprehensive remote sensing, geophysical,

[00:09:07] and in-situ measurements ever performed at Jupiter. To bring JUICE to life, ESA has led a consortium

[00:09:15] of more than 2,000 people in 23 countries, working in 18 institutions and 83 companies.

[00:09:23] NASA, the Japan Aerospace Exploration Agency, and the Israel Space Agency have all supplied

[00:09:30] hardware. For eight years, JUICE will cruise through space before beginning a complex series

[00:09:36] of maneuvers in the Jupiter system. During this time, JUICE will face many dangers.

[00:09:42] Radiation near Jupiter can fry the spacecraft's electronic brain. The planet's gravitational

[00:09:49] pull is so large it could threaten derailment. Nevertheless, ESA's expert spacecraft operators

[00:09:57] will guide JUICE through 35 flybys of Europa, Ganymede, and Callisto before orbiting Ganymede.

[00:10:05] But the dangers will be worth it for the science that JUICE will uncover.

[00:10:10] Europa and Ganymede are thought to contain subsurface oceans that could hold more water

[00:10:15] than Earth's oceans. JUICE will explore these moons to study whether life could arise in

[00:10:21] different environments across the cosmos. JUICE will also study Jupiter's complex weather,

[00:10:28] chemistry, and climate in detail. It will turn Jupiter into a standard reference for us to compare

[00:10:35] against other gas giant planets throughout the cosmos.

[00:10:42] This is Space Time. Still to come, Russia tests their new heavy lift Angara rocket,

[00:10:48] and later in the Science Report, a new study shows that junk food has been linked to a higher

[00:10:53] risk of over 30 different physical, mental health, and sleep problems. All that and more still to

[00:10:58] come on Space Time. The Kremlin have undertaken a successful test launch of Russia's new heavy

[00:11:19] lift Angara A-5 rocket. The flagship A-5 is a more powerful version of the Angara family of

[00:11:25] rockets. They've been developed to replace the old Soviet-designed Proton rockets, which together

[00:11:30] with the even older Soyuz rockets have been the workhorses of the Russian space program for

[00:11:35] decades. The three-stage Angara A-5 is designed to carry up to 24.5 tonnes into LEO or low Earth

[00:11:42] orbit and 5.4 tonnes into geostationary transfer orbit. The test flight was carried out from

[00:11:49] Moscow's Vostochny Cosmodrome in Russia's Far East. Two earlier launch attempts during the week

[00:11:54] were scrubbed. Yuri Borisov, head of the Russian Federal Space Agency at Roscosmos, says the first

[00:11:59] attempt to launch was cancelled just two minutes before liftoff due to the failure of a pressurization

[00:12:05] system for the oxidizer tank in the central block of the rocket. He says a second launch attempt

[00:12:10] the next day was aborted by the automatic safety system which registered a flaw in the engine start

[00:12:15] control mechanism. This test flight was only the fourth flight of the Angara A-5 in 10 years.

[00:12:22] The program has been beset with technical issues, funding problems and quality control concerns.

[00:12:28] The previous test flight was only deemed partially successful when the upper stage

[00:12:33] failed to restart for a second engine burn. All of the three previous test launches were carried out

[00:12:38] from the Plesetsk Cosmodrome north of Moscow. This is Space Time, and time now to take another brief

[00:13:00] look at some of the other stories making use in science this week with the Science Report.

[00:13:06] A new study warns that up to 246 million older adults around the world are projected to be

[00:13:11] exposed to dangerous acute heat by the year 2050, with those living in Asia and Africa experiencing

[00:13:17] the most severe effects. The findings reported in the journal Nature Communications claims that

[00:13:23] by 2050 more than 23 percent of the global population aged over 69 were living climates

[00:13:29] with acute heat exposure greater than the critical threshold of 37.5 degrees Celsius

[00:13:34] compared with the 14 percent in 2020. The authors suggest that areas with aging populations and

[00:13:40] rising heat exposures are likely to face considerable demands for social health services

[00:13:45] and policies will need to be developed to accommodate this. Scientists have found that

[00:13:50] eating more junk food such as packaged snacks, sodas and sugary cereals is associated with a

[00:13:56] higher risk of more than 30 different physical, mental health and sleep problems. The findings,

[00:14:02] reported in the British Medical Journal, combine the results of 45 previous meta-analysis studies.

[00:14:08] The study's authors say that while this kind of research can't prove that junk food is causing

[00:14:12] health problems, there was consistent evidence that ultra-processed foods are associated with

[00:14:17] death and specific conditions including type 2 diabetes, obesity, anxiety, sleep problems and

[00:14:24] wheezing. When it comes to believing in playground gossip, it seems even young kids rely on multiple

[00:14:30] sources to verify the gossip. The findings reported in the Journal of the Royal Society

[00:14:35] Open Science looked at 107 year olds who were told either positive, neutral or negative gossip

[00:14:41] from a group of puppets before allocating sticker rewards to the subject of the gossip.

[00:14:46] It took positive gossip from multiple informants to impact their choice of reward.

[00:14:51] The kids would act straight away on negative gossip, whether it came from one or multiple sources,

[00:14:55] although they were more likely to trust negative gossip that came from more than one source.

[00:15:00] The authors say the study shows that kids are sensitive to objective indicators such as the

[00:15:05] number of gossip sources when determining a piece of gossip's credibility. There's been another

[00:15:12] Bigfoot sighting, this one in the city of Manchester, England. Tim Mindham from Australia

[00:15:17] Skeptic says this one was actually more of a Bigfoot feeling than an actual sighting.

[00:15:22] Bigfoot, Sasquatch, Yeti, Yowie, whatever you like to call it, appears supposedly all around

[00:15:29] the world. There's a lot of countries which claim to have tall hairy men. So later seeing a fisherman

[00:15:34] in the UK near Manchester by a stream at night by himself, sounds a bit creepy, had a feeling

[00:15:40] of being watched. Therefore, he didn't actually see anything but he thought there was something

[00:15:44] there. So that becomes proof of Bigfoot in the UK. This fellow was also a bit of a, he had reported

[00:15:50] other paranormal events in the past. Of course, yes. He's a bit prone to this. So this became a bit

[00:15:56] of an interesting story. The pro-Bigfooters naturally took it up and said, see this is proof

[00:16:02] and others keep showing photos and they're always terrible photos of some shapes behind a lot of

[00:16:07] trees. Squatch blobs, they're called squatch blobs. Yes, okay. Bigfoot in the UK, not the only Bigfoot

[00:16:13] in the UK. There have been other sightings as there have been sightings all around the world.

[00:16:16] No evidence apart from sightings and the occasional blurry photos and occasional sloppy footprint in

[00:16:21] a soft soil. Apart from that, no dead Bigfeet, no little Bigfoot, no family of Bigfoot which you'd

[00:16:28] need a lot of families to actually keep going with a population. One Bigfoot does not a civilization

[00:16:33] make, they will die and that'll be the last of the Bigfoot. So Bigfoot male or female, they need

[00:16:38] mates of some sort and they have kids and you have to feed them and it's unlikely that one sole

[00:16:45] Bigfoot is going to be the answer to everything. These pop up all the time. Someone was supposedly

[00:16:49] seeing a Bigfoot nest which is a bit like gorillas but they have a nest which is basically like a

[00:16:53] cradle. These Bigfoot nests are more like a little tent made out of twigs and things. They can climb

[00:16:58] in and out. Let's find one, let's find some real fur, let's find a Bigfoot body and then we'll be

[00:17:03] a lot closer to them. You want DNA, that's what you're saying. You want DNA and you want Bigfoot

[00:17:07] DNA not deer DNA or bear DNA or koala DNA. That's Tim Mendham from Australian Skeptics

[00:17:15] and that's the show for now. Space Time is available every Monday, Wednesday and Friday

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