Pollution may give ‘first’ stars a youthful look

Some of the oldest stars in the universe might be lurking in the Milky Way. No one has identified them yet, however, because they simply don’t look their age. A cosmetic disguise makes them appear too youthful. A new study finds that it’s like we’re viewing them through a face mask: nearly 13 billion years of cosmic pollution.

Shortly after the Big Bang, the first stars were born. They were made of only hydrogen and helium. These elements are the lightest on the periodic table. Heavier elements were forged inside later generations of stars. All of the stars now known, including the sun, belong to those later generations. Astronomers have yet to find any pristine, early stars. But they think that some are still out there, waiting to be found.

Some first-generation stars might even be scattered throughout our galaxy, the Milky Way, according to new computer models. Scientists haven’t found any because exposure to interstellar dust and gas would make those stars look younger than they are, says Jarrett Johnson. He is an astronomer at Los Alamos National Laboratory in New Mexico. He described those simulations in the November 1 issue of the Monthly Notices of the Royal Astronomical Society.

The vast expanse of the universe may look empty, but it contains a lot of gas and dust. Johnson calculated how the slow, steady rain of that debris might change the makeup of early stars. Starlight would push back on some dust grains, he finds. But the incoming gas would be unstopped. It would pollute the star, seeding it with an abundance of new, bigger elements. Among such pollutants: carbon and oxygen. Their presence would disguise the oldest stars. Now they would look like later-generation suns. Yet the elements in dust, such as titanium and iron, would be mostly missing.

The calculations make several assumptions. One is how interstellar chemistry has changed over the age of the universe. But, “we have to start somewhere and this is a really good effort,” says Anna Frebel. She is an astronomer at the Massachusetts Institute of Technology in Cambridge.

Searching for very old stars “is a numbers game,” she notes. There probably aren’t many of these ancient stars left. That means astronomers may have to spend years combing through the galaxy for one. Recent calculations indicate that to find a single primordial star in the Milky Way, researchers would need to look at about 20 million stars!

Frebel and other researchers have found several stars that roughly resemble Johnson’s predictions. But none appear quite right. For instance, these are relatively abundant in titanium, she say. And the calculations suggest that polluted first-generation stars should have very little.

Power Words

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

Big Bang  The rapid expansion of dense matter that, according to current theory, marked the origin of the universe. It is supported by physics’ current understanding of the composition and structure of the universe.

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.

chemistry   The field of science that deals with the composition, structure and properties of substances and how they interact with one another. Chemists 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) The term is used to refer to the recipe of a compound, the way it’s produced or some of its properties.

cosmic    An adjective that refers to the cosmos — the universe and everything within it.

debris  Scattered fragments, typically of trash or of something that has been destroyed. Space debris, for instance, includes the wreckage of defunct satellites and spacecraft. 

element  (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.

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.

helium  An inert gas that is the lightest member of the noble gas series. Helium can become a solid at -458 degrees Fahrenheit (-272 degrees Celsius).

hydrogen The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues.

interstellar Between stars.

oxygen  A gas that makes up about 21 percent of the atmosphere. All animals and many microorganisms need oxygen to fuel their metabolism.

periodic table of the elements  A chart (and many variants) that chemists have developed to sort elements into groups with similar characteristics. Most of the different versions of this table that have been developed over the years tend to place the elements in ascending order of their mass.

primordial   An adjective that refers to something that goes back to the beginning of time or to the earliest existence of something.

simulate To deceive in some way by imitating the form or function of something. A simulated dietary fat, for instance, may deceive the mouth that it has tasted a real fat because it has the same feel on the tongue — without having any calories. A simulated sense of touch may fool the brain into thinking a finger has touched something even though a hand may no longer exists and has been replaced by a synthetic limb. (in computing) To try and imitate the conditions, functions or appearance of something. Computer programs that do this are referred to as simulations.

star  Thebasic 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.

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. Or a sunlike star.

universe The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).