Cool Job: Making stellar connections | Science News for Students

Cool Job: Making stellar connections

Astrophysicist Paula Jofré reaches across disciplines to link stars across the galaxy
Oct 12, 2018 — 6:45 am EST
a photo of Paula Jofré

Astrophysicist Paula Jofré wants to find links between all the stars in our galaxy, the Milky Way.  


Paula Jofré wants to map the galactic lineage of every star in the Milky Way. It’s like tracing your family tree — if, that is, your grandparents were the exploding stars we call supernovas.

Jofré is an astrophysicist at Universidad Diego Portales in Santiago, Chile. There, she studies the inner lives and histories of stars. She measures the wavelengths of light these stars emit. That shows her which chemical elements the stars contain. That also tells her the proportions of those elements in each star.

Inspiration from art and biology

The scientist then does something unusual. Borrowing a technique from biology, she traces how the stars evolved.

Biologists can examine the DNA in ancient human remains to trace a population’s history. Jofré does something similar with stars. She uses the composition of modern stars to track how their ancestors moved around our galaxy, the Milky Way. Her best-known work, and the research of which she’s most proud, uses those elements to chart the first family tree of stars in the Milky Way.

She got the idea while a postdoc. She was attending an event at the University of Cambridge in England. It had been organized by an art history student. The focus was how scientists visualize their results. There, Jofré met Cambridge anthropologist Robert Foley. He showed her how evolutionary trees can link relationships between members of a species over time. Stars, Jofré realized, also pass down bits of themselves to successive generations. Perhaps, she thought, those generations could be traced back in time.

She and Foley soon hashed out the stellar family tree project while at dinner in a Cambridge dining hall. (The hall is “very much like a Harry Potter room,” she recalls. All the fellows even wear academic gowns that look similar to Hogwarts robes.) Stars obviously don’t procreate like animals, the pair agreed. However, dying stars do pass on their chemistry, much like parents pass along parts of their DNA to their children.

That happens because stars forge heavy elements, such as carbon and iron. When the stars die, they often explode, spreading those newly formed elements throughout the cosmos. The next generation of stars are born from collapsing clouds of gas containing those elements. That lets them pick up elements from the earlier generation.

And thus, a family is born.

Stars from the same gas cloud should have almost the same chemistry. That’s similar to how siblings share a lot of the same DNA. The analogy is close enough that Jofré, Foley and their colleagues built a three-branched tree showing the relationships of 21 stars that are siblings of the sun. They described it last year in the Monthly Notices of the Royal Astronomical Society.

The team also reported that two of the branches were known groupings. One was the Milky Way’s thin disk of stars. The other was an older thick disk that surrounds it. The third branch revealed new connections. That showed that Jofré’s technique does more than map known star relationships. The approach can reveal new information about past stellar nurseries. (Stellar nurseries are places where stars are born.)

All in the family

Paula Jofré and her colleagues borrowed tools from biology to map out chemical relationships between the sun and 21 of its sibling stars. Three main branches emerged: younger stars in the Milky Way’s thin disk (red, including the sun), much older stars that could be in the Milky Way’s more dispersed thick disk (dark blue) and a third branch that lies in between (light blue). Six stars (black) had no clear relationship to the others. More observations could help tie them in.

a tree of stars in the Milky Way
Source: P. Jofré et al/Monthly Notices of the Royal Astronomical Society 2017; Credit: T. TIBBITTS

By expanding this approach to more groups of stars, “we could use these trees to learn something about the evolution of our whole galaxy,” Jofré says. “That has been so exciting.”

Jofré sees what other astronomers don’t

This approach is original and inventive, if a little unusual, other astronomers say.

“Paula Jofré impressed me as being very innovative,” says Kenneth Freeman. He’s an astronomer at the Australian National University in Canberra. “She sees things that other researchers do not see.”

Payel Das, of the University of Oxford, is a collaborator on the Milky Way project and a close friend. She calls Jofré “really brave” as a researcher. “She’s very confident, which is really nice. I think especially now — we’re going through this crisis of women in physics and science and all this — we need this confidence.”

Jofré has never shied away from unpopular paths. Before she graduated from an all-girls high school in Santiago, a guidance counselor spoke to her class. That counselor talked about the importance of choosing a career that would leave time for family. She said one shouldn’t, for instance, choose a career in astronomy.

“The whole class looked at me,” Jofré recalls. They knew she had been interested in astronomy since childhood. But that moment only strengthened her resolve. “This woman trying to say, please don’t do that, was for me argument to say, please do it.”

The question of whether astronomy was compatible with a family came up sooner than Jofré expected. Her first child was born before she and her partner, Thomas Maedler, finished their PhDs. Their second was born during her first postdoctoral fellowship. Being the only parents in their group of graduate students was difficult. “You feel quite lonely when you’re the only one,” Jofré says.

But contrary to the guidance counselor’s warnings, parenthood has been grounding for the two. It has even helped keep them focused on what’s important. “We’re always this little nucleus, the four of us — this little atom that is walking around,” Maedler says.

For Jofré, science has been inextricably entwined with family — not just the sun’s, but her own.

Power Words

(more about Power Words)

academic     Relating to school, classes or things taught by teachers in formal institutes of learning (such as a college).

astronomy     The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.

astrophysics     An area of astronomy that deals with understanding the physical nature of stars and other objects in space. People who work in this field are known as astrophysicists.

atom     The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

biology     The study of living things. The scientists who study them are known as biologists.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemistry     The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) Chemistry also is used as a term to refer to the recipe of a compound, the way it’s produced or some of its properties. People who work in this field are known as chemists.

cloud     A plume of molecules or particles, such as water droplets, that move under the action of an outside force, such as wind, radiation or water currents.

colleague     Someone who works with another; a co-worker or team member.

cosmos     (adj. cosmic) A term that refers to the universe and everything within it.

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

element     A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

evolution     (adj. evolutionary) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the particular conditions in which it developed. Or the term can refer to changes that occur as some natural progression within the non-living world (such as computer chips evolving to smaller devices which operate at an ever faster speed).

forge     (noun) A furnace or shop where metal is worked and turned into new materials. (verb) To shape metals under heat and/or pressure, or (colloquially) to form one element from another under the intense heat and pressure inside stars.

galaxy     A massive group of stars bound together by gravity. Galaxies, which each typically include between 10 million and 100 trillion stars, also include clouds of gas, dust and the remnants of exploded stars.

generation     A group of individuals (in any species) born at about the same time or that are regarded as a single group. Your parents belong to one generation of your family, for example, and your grandparents to another. Similarly, you and everyone within a few years of your age across the planet are referred to as belonging to a particular generation of humans. The term also is sometimes extended to year classes of other animals or to types of inanimate objects (such as electronics or automobiles).

heavy element     (to astronomers) Any element other than hydrogen (or possibly helium).

high school     A designation for grades nine through 12 in the U.S. system of compulsory public education. High-school graduates may apply to colleges for further, advanced education.

iron     A metallic element that is common within minerals in Earth’s crust and in its hot core. This metal also is found in cosmic dust and in many meteorites.

Milky Way     The galaxy in which Earth’s solar system resides.

nucleus     (in astronomy) The rocky body of a comet, sometimes carrying a jacket of ice or frozen gases. (in physics) The central core of an atom, containing most of its mass.

PhD     (also known as a doctorate) A type of advanced degree offered by universities — typically after five or six years of study — for work that creates new knowledge. People qualify to begin this type of graduate study only after having first completed a college degree (a program that typically takes four years of study).

physics     The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. A scientist who works in such areas is known as a physicist.

population     (in biology) A group of individuals from the same species that lives in the same area.

postdoctoral scholar, or post-doc     A research position for people who have just completed their doctorate in some field of study. It allows the individual to acquire new skills or pursue new lines of research on the road to a research career.

proportion     The amount of a certain component of a mixture relative to other components. For example, if a bag contains 2 apples and 3 oranges, the proportion of apples to oranges in the bag is 2 to 3.

sibling     An offspring that shares the same parents (with its brother or sister).

star     The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

stellar     An adjective that means of or relating to stars.

sun     The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.

supernova     (plural: supernovae or supernovas) A massive star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass.

wavelength     The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.


Journal:​ P. Jofré et al. Cosmic phylogeny: reconstructing the chemical history of the solar neighbourhood with an evolutionary treeMonthly Notices of the Royal Astronomical Society. Vol. 467, May 11, 2017, p. 1140. doi: 10.1093/mnras/stx075.