Sun sibling spotted

A star in the constellation Hercules may be a sister to our sun, astronomers report in a new study. Called HD 162826, it is among an estimated 1,000 to 10,000 stars born at the same time as our sun and from the same cloud of dust and gas.

Just as children grow up and move on, HD 162826 is no longer close to her sibling. It shines from some 110 light-years away. That means its light takes 110 years to reach Earth.

Iván Ramírez, an astronomer at the University of Texas at Austin, led the experiment to identify the star. He and his co-workers are developing a way to identify other stellar siblings. Their work might one day point to the birthplace of our solar system. It also could help identify under what conditions it formed. The solar system is composed of Earth and seven other planets that orbit the sun, together with asteroids, comets and other debris.

Like most stars, the sun and its siblings emerged from a nebula — a giant cloud of dust and gas in space. Over time, those star siblings scattered throughout our galaxy, the Milky Way. Sifting through all the stars in the Milky Way to identify which are siblings would take too long. So Ramírez and his team sought a more manageable way.

They reasoned that a star should be made of the same stuff as its parent nebula. And any stars born within that nebula also should share the same chemical makeup. So, to look for siblings of the sun, the astronomers first looked for stars made of the same mix of elements. The team reported its findings May 8 on arXiv.org. (The website allows physicists and other scientists to share their work.) The study will be published in a future issue of Astrophysical Journal.

Ramírez and his colleagues studied starlight. They recorded it using instruments on two telescopes, one in Texas and the other in Chile. Light can reveal a star’s composition. Although it may look white from Earth, that light actually is a spectrum. A spectrum is a band of colors, as in a rainbow. Astronomers use a device called a spectrograph to separate white light into its spectrum. Different elements in a star will absorb different colors (or light wavelengths). So the light from the star will lack some colors. By studying which wavelengths are missing, astronomers can “see” which elements make up a star.

With a spectrograph, the astronomers probed 30 stars. A few had the same amount of iron — an element commonly found in stars — as the sun. The abundances of some other elements also matched those in the sun. Then they narrowed their search further, looking for stars that move in roughly the same direction as our sun.

“Most stars separate really quickly and keep going away from the sun,” Ramírez told Science News. However, the star’s sibling seemed to follow the sun’s path around the galaxy.

HD 162826 also was born at about the same time as our sun. One way astronomers estimate a star’s age is by its brightness and color. In the new study, Ramírez and his team estimate the age of HD 162826 at 4.6 billion years old. That is very close to the sun’s age: 4.57 billion years old.

“The fact that these guys found [a sibling to the sun] is not crazy,” Fred Adams told Science News. An astrophysicist at the University of Michigan in Ann Arbor, he did not work on the new study. Researchers had predicted that astronomers should be able to find siblings in the sun’s cosmic neighborhood.

Power Words

asteroid  A rocky object in orbit around the sun. Most orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.

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.

astrophysics  An area of astronomy that deals with understanding the physical nature of stars and other objects in space.

comet  A celestial object consisting of a nucleus of ice and dust. When a comet passes near the sun, gas and dust vaporize off the comet’s surface, creating its trailing “tail.”

constellation  Patterns formed by prominent stars that lie close to each other in the night sky. Modern astronomers divide the sky into 88 constellations, 12 of which (known as the zodiac) lie along the sun’s path through the sky over the course of a year.

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

element  (inchemistry)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. Our galaxy is called the Milky Way.

light-year  The distance light travels in a year, about 9.48 trillion kilometers (almost 6 trillion miles). To get some idea of this length, imagine a rope long enough to wrap around the Earth. It would be a little over 40,000 kilometers (24,900 miles) long. Lay it out straight. Now lay another 236 million more that are the same length, end-to-end, right after the first. The total distance they now span would equal one light-year.

nebula    A cloud of space gas and dust existing between major adult stars. Telescopes can detect these clouds by the light they emit or reflect. Some nebulas also appear to serve as the nurseries in which stars are born.

planet  A celestial object that orbits a star and is big enough for gravity to have squashed it into a roundish ball. It also must have cleared other objects out of the way in its orbital neighborhood. To accomplish the third feat, it must be big enough to pull neighboring objects into the planet itself or to slingshot them around the planet and off into outer space. Astronomers of the International Astronomical Union (IAU) created this three-part scientific definition of a planet in August 2006 to determine Pluto’s status. Based on that definition, IAU ruled that Pluto did not qualify. The solar system now consists of eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

solar system  The eight major planets and their moons in orbit around the sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

spectrograph  An instrument used to record light and separate it into its spectrum.

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.

telescope  A light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.

wavelength  The distance between one peak and the next in a series of waves, or the distance between one trough and the next. 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.