Newfound stars rank as farthest and one of the smallest | Science News for Students

Newfound stars rank as farthest and one of the smallest

It would take more than a backyard telescope to spot them
Aug 1, 2017 — 7:00 am EST
star Saturn

The star EBLM J0555-57Ab (illustrated, right) is one of the smallest ever found. It has a radius similar to Saturn’s (illustrated, left). The star’s mass is just large enough that it can fuse hydrogen in its core.

COURTESY OF UNIV. OF CAMBRIDGE

Astronomers scanning the skies with powerful telescopes have found two record-setting stars. One is the most distant star ever observed. The other ranks as one of the tiniest. That second is so small that it can barely burn.

The light from the farthest star traveled across two-thirds of the universe. That puts the star a whopping 9 billion light-years away. That blows away the previous record holder. The previous farthest star observed directly was a mere 55 million light-years away.

Hubble stars
One of the faint points of light just above and to the left of the super bright central star in this image is the farthest star known. The gravity of the huge galaxy cluster MACS J1149 bent the light from the bright blue star, letting it reach us from 9 billion light-years away.
NASA, ESA, S. RODNEY (JHU) AND THE FRONTIERSN TEAM; T. TREU (UCLA), P. KELLY (UC BERKELEY) AND THE GLASS TEAM; J. LOTZ (STSCI) AND THE FRONTIER FIELDS TEAM; M. POSTMAN (STSCI) AND THE CLASH TEAM; Z. LEVAY (STSCI)

Patrick Kelly is an astronomer at the University of California, Berkeley. He and his colleagues found the star in images from the Hubble Space Telescope. They were scanning images of a galaxy cluster known as MACS J1149. In April and May 2016, Kelly and his team saw a mysterious dimming and brightening in one point of light. It was in the galaxy cluster’s vicinity.

The team looked at follow-up images and made analyses, which they posted June 30 at arXiv.org. Those analyses showed that the light is probably from a single bright blue star. That star is behind the galaxy cluster and aligned along Hubble’s line of sight.

The star was visible only because of a phenomenon called gravitational lensing. The gravity of an object like the galaxy cluster is so huge that it bends the spacetime around it. That makes it act like a cosmic magnifying glass. Astronomers can use these objects to observe things like stars that are more distant than telescopes can see on their own.

The team calculated how much the star’s light was stretched by its journey. That was a clue to its extreme distance. Since the universe is 13.8 billion years old, that means this star’s light has crossed 65 percent of the universe to reach us.

Itty-bitty star

Scientists have also just turned up one of the smallest stars ever seen. Its discoverers all worked on a project known as the Wide Angle Search for Planets, or WASP. These astronomers use ground-based telescopes in Spain and South Africa to monitor the skies. The newfound one is quite small. Its radius is only about the size of Saturn’s.

The mini star has a very long name: EBLM J0555-57Ab. Its about the size of a previously reported runt, which also has a big name (2MASS J0523-1403).Both are much smaller than the Jupiter-sized TRAPPIST-1. That peewee star recently gained renown for hosting seven Earth-sized planets.

Although the newfound mini star’s girth is similar to a planet’s, it is much heftier. It has almost 300 times Saturn’s mass. Still, that’s only about 8 percent of the sun’s mass. That means that the object barely meets the qualifications for being a star, scientists reported July 12 in Astronomy & Astrophysics. By that they mean that the star just meets the limit at which nuclear fusion can occur in a star’s core. (Nuclear fusion is the process that fuels a star.) If the star were less massive, it would instead be a failed star known as a brown dwarf.

The miniature star orbits another, larger one. WASP scientists detected the star with a method typically used to scout for exoplanets. They watched it pass in front of its companion and dim the larger star’s light.

Power Words

(for more about Power Words, click here)

angle     The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.

arXiv     A website that posts research papers — often before they are formally published — in the fields of physics, mathematics, computer science, quantitative biology, quantitative finance and statistics. Anyone can read a posted paper at no charge.

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.

brown dwarf     A would-be star that never became massive enough to sustain nuclear fusion and burn brightly.

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

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

exoplanet     Short for extrasolar planet, it’s one that orbits a star outside our solar system.

fuel     Any material that will release energy during a controlled chemical or nuclear reaction. Fossil fuels (coal, natural gas and petroleum) are a common type that liberate their energy through chemical reactions that take place when heated (usually to the point of burning).

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.

galaxy cluster     A group of galaxies held together by gravity. Galaxy clusters are the largest known objects in the universe.

gravitational lensing     The distortion of light by an intense gravitational force, such as what can be exerted by clusters of galaxies — the most massive things in the universe. The gravity can bend or focus light, making it appear brighter and in one or more different places in the sky.

gravity     The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.

Jupiter     (in astronomy) The solar system’s largest planet, it has the shortest day length (10 hours). A gas giant, its low density indicates that this planet is composed of light elements, such as hydrogen and helium. This planet also releases more heat than it receives from the sun as gravity compresses its mass (and slowly shrinks the planet).

light-year     The distance light travels in one 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.

mass     A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.

nuclear fusion     The process of forcing together the nuclei of atoms. This fusion is the phenomenon that powers the sun and other stars, producing heat and forging the creation of new, larger elements.

orbit     The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.

phenomenon     Something that is surprising or unusual.

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood.

radius     A straight line from the center to the circumference of a circle or sphere.

runt     An organism that starts its life much smaller than usual, and may stay smaller than normal into adulthood. 

Saturn     The sixth planet out from the sun in our solar system. One of the four gas giants, this planet takes 10.7 hours to rotate (completing a day) and 29 Earth years to complete one orbit of the sun. It has at least 53 known moons and 9 more candidates awaiting confirmation. But what most distinguishes this planet is the broad and flat plane of seven rings that orbit it.

spacetime   A term made essential by Einstein’s theory of relativity, it describes a designation for some spot given in terms of its three-dimensional coordinates in space, along with a fourth coordinate corresponding to time.

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.

telescope     Usually 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.

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).

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Citation

Journal:​ ​​A. von Boetticher et al. A Saturn-size low-mass star at the hydrogen-burning limit. Astronomy & Astrophysics. Published online June 12, 2017. doi: 10.1051/0004-6361/201731107.

Journal:​ ​​P.L. Kelly et al. An individual star at redshift 1.5 extremely magnified by a galaxy-cluster lens. arxiv.org. Published online June 30, 2017.