Discovery of a second-generation star
from the early Universe
And yes, we have done it again. It’s a new record holder for the most iron-poor star! :)
This star, SM0313, formed within the second generation of stars in the universe, soon after the very first stars exploded. We determined its chemical abundances of this stars to find out from what kind of gas cloud this object formed. The abundances are so low that only one first star could have provided the elements to the cloud when it exploded as one of the first ever massive supernova.
Using the stellar chemical abundances is the best and most exciting way to reconstruct the nature and properties of the short-lived elusive first stars and their explosions.
A more detailed video (English+German) and written summaries as well as some images can be found below. Enjoy!
Read the original publication
“A single low-energy, iron-poor supernova as the source of metals in the star SMSSJ031300.36-670839.3” by Keller, Bessell, Frebel, et al. 2014, published in Nature 508 (Febuary 27 issue). This is work done by MIT astronomers Anna Frebel and Dr. Heather Jacobson in collaboration with astronomers around Stefan Keller from Mt. Stromlo Observatory of the Australian National University in Canberra, Australia.
Short video explanation of this amazing new discovery (NEW)
Listen to Anna Frebel explain the search for the oldest, most metal-poor stars and what this new discovery means (in English). A written summary is also given below.
Hier erklärt Anna Frebel die Suche nach den ältesten und metallärmsten Sternen und was die neue Entdeckung bedeutet (auf Deutsch). Wenn Sie mehr zur Suche nach den ältesten Sternen wissen möchten, gibt es hier genau das richtige Buch für Sie!
The videos were produced by Gerhard Huber. More information about his beautiful photos and video/film documentations can be found here. / Die Videos wurden von Gerhard Huber produziert. Weitere Informationen zu seinen Fotos und Video/Film-Dokus gibt’s hier.
Here is another introductory lecture of the Genesis of the Elements and Cosmic Chemical Evolution given at the Kavli Frontiers of Science Meeting, Irvine, CA, Aug 2014.
And here is a recent podcast (January 2014) done with astronomers from McGill University (Montreal, Canada) where I talk about searching for the oldest stars.
Curious? Information about the star
Name: SMSSJ031300.36-670839.3; SMSS stands for SkyMapper Southern Sky Survey; the 031300 refers to the right ascension of the star on the sky, RA=03h 13min 00.36sec; -670839.3 refers to the declination of Dec=-67degree 08arcmin 39.3 arcsec. From the coordinates you can ‘read’ off that the star is very southern (can only be seen from the Southern hemisphere) and that it’s visible early on in the year. The nickname of the star is SM0313.
Location: SM0313 is located in the Southern constellation Hydrus (small watersnake).
Distance: Several thousand light years out into the halo of the Milky Way (distance measurements are difficult).
Brightness: Apparent visual magnitude of V=14.7.
Discovery: SM0313 was found among 60 million stars surveyed with the SkyMapper telescope. But data from two more telescopes (the ANU 2.3m telescope in Australia and the 6.5m Magellan telescope in Chile) were required to complete the discovery and confirm the extraordinary nature of this star.
Fun Fact: The mass in iron in this stars is less than 0.01% of the Earth iron core which is 1% of the Moon’s mass. But the star is one million times bigger that the Earth!
[If the Moon was made from iron and you’d throw less than 1% of it into a hydrogen-helium gas ball a little smaller than the Sun, you’d made SM0313 :)]
Is SM0313 is the oldest star we know? Truthfully, we don’t actually know how old SM013 is. This is because, sadly, we can’t determine a specific age of these kinds of objects. However, the chemical composition of SM0313 tells us that it is a second-generation star in the Universe which naturally makes this star nearly as old as the universe itself.
Researchers identify one of the earliest stars in the universe MIT press release
Australians discover oldest star ANU press release
Astronomers discover oldest star Monash University press release
Here are a few selected articles:
The Archaeology of the Stars (with podcast) New York Times
Stellar archaeologist: We excavated the purest star New Scientist
Discovery of ancient star offering clues about infant universe Christian Science Monitor
The Purest Star Tells an Ancient Tale Sky & Telescope
Sternenjägerin spürt älteste bekannte Sonne auf Die Zeit online (in German)
Stellarer Methusalem in kosmischer Nachbarschaft Telepolis (in German)
Deutsche Astronomin entdeckt ältesten Stern Futurezone.at (in German)
Note that any ages for the star listed in these articles are not correct! We cannot determine the age of this star, we can only say that it is a second-generation star (and thus presumably almost as old as the universe itself). Here is a great article by Geraint Lewis (Univ. of Sydney) that discusses this topic in a science and cultural context.
Just google and you’ll find plenty more articles!
Here is a popular science summary of our new discovery
The oldest stars are ~13 billion years old and formed as part of the first generations of stars in the universe. Due to the long live times these low-mass stars are still shining today not too far out in the Milky Way. We have a large search program in place to find these ancient fossil stars to learn about the earliest times of the universe and the conditions of star formation back then.
All chemical elements heavier than hydrogen and helium we know from the Periodic Table were successively made in stars and supernova explosions since the Big Bang (which left a universe just made from hydrogen and helium). Hence, the oldest stars can be identified through their tiny amounts of these heavier elements such as carbon and iron: Low abundance then indicates early formation time in the universe. Additionally, low mass stars preserve the elemental composition of their birth gas cloud in their surface for many billion years. We thus discover the oldest stars through determining their chemical composition of many elements, such as carbon and iron and then concentrating on those stars with the lowest abundances of these elements.
By studying the chemical abundances in detail we can thus learn about conditions of the stellar birth place. Moreover, we have an opportunity to reconstruct what kind of supernova explosions actually created the elements that we observe in our oldest stars today.
Our paper describes the discovery of a new star which has and extremely such tiny iron abundance. This implies that the star is a true second-generation star in the universe. Only one massive, short-lived star of the very first generation of stars in the universe provided all the observed elements when it exploded as one of the first ever supernova explosions shortly after the Big Bang. An interesting controversy, however, is that the star shows a much large abundance in carbon, compared to its tiny iron concentration. Different element ratios, such as the carbon-to-iron ratio give then specific clues to the element-creating nucleosynthesis processes that operated in the star when it exploded.
Implications of this discovery are far reaching because we find this supernova to have been very massive (60 times the mass of the Sun) and of lower-than-expected explosion energy compared to supernova explosions observed today. The large carbon abundance indicates that this element was an element of fundamental importance not just for life but already in the early universe (“from day 1” so to say). Moreoever, we have been searching for second-generation stars for a long time. This first unambiguous discovery of a second-generation stars in the universe demonstrates that our new search strategy is working extremely well. This has opened a new door for finding more of these rare and precious fossils that teach us in a unique way about what the short-lived generation first stars in the universe were like and how star and galaxy formation began to light up the universe ~13 billion years ago.
We have used MIT’s access to the 6.5m Magellan Telescope in Chile to collect ~50% of the data with the MIKE spectrograph used in our analysis. The other half of the data came from a Magellan Telescope allocation provided by the colleagues from the Australian National University. MIT postdoctoral fellow Dr. Heather Jacobson traveled to chile to carry out the MIT observations of this star.
Here is a picture of SM0313. It’s the fuzzy blob in the center of the image. Not very interesting or inspiring, really.
Although a picture is usually worth a thousand words…
… a spectrum is worth a thousand pictures
The spectrum of SM031 hardly contains any absorption lines in its spectrum. The strong lines you can see are from hydrogen, and carbon (at 4300A) and from the Earth atmosphere (at 5800 and 6300A; not from the star itself). For comparison, the young metal-rich Sun would have thousands and thousands of dark lines. Only a spectrum provides information of the detailed chemical composition of an object.
Videos about observing with the Magellan Telescopes in Chile — get insight into astronomer’s work
Using the Magellan Telescopes in Chile extraordinary nature of SM0313 was discovered. If you are interested in seeing what it’s like to do such observations in Chile with the Magellan Telescopes check out the following videos:
Meet the Clay Telescope The telescopes are cared for 24/7 by technicians, engineers and software experts to ensure that everything works smoothly for night time observing. In this video you’ll see the Clay Telescope (the left one in the previous video) and how its secondary and tertiary mirror get refitted to work for a different suite of instruments to be used by astronomers for their observing. It also gives you a sense of how large these telescopes are – the primary mirror of this telescope is 6.5 meters in diameter. These changes took about a day.
Observing with the Magellan Telescope When it’s clear, observers are happy to observe all night long (as in 10-12h)! See what a a nights at the telescope look like. Can you spot the newly taken spectra on the screens?
Catch some stars When it’s cloudy or it rains, observers aren’t happy because they have to wait until the clouds have passed. But it makes for a great video when the clouds are thin and patchy. When the weather is less cooperative, one can still try to observe as stars can still be seen behind the clouds. Watch for the Southern Cross, Scorpio and the many trucks on the horizon that pollute the dark sky all night long.
Trying to observe… Here is another video showing how conditions can rapidly change on the mountain. All you can do is watch.
Some other short clips are available here (my YouTube Channel)
We used the telescope on the left, the Clay Telescope, for our observations. The Milky Way with its luminous Galactic center can ben seen on the sky in between the two twin Magellan telescopes.