Yoda’s words about the Force in Star Wars: The Empire Strikes Back may ring a bell for sci-fi fans. “That energy surrounds us and connects us.” Real matter consists of tiny dust particles that envelop every star in the universe. Referred to as interstellar matter (ISM), these particles, while not as magical as energy fields granting telekinesis, play a crucial role in star formation.
Contrary to the dust found on bookshelves or spiderwebs, interstellar dust is akin to smoke from a campfire: individual particles too small to see, but visible when they amass into clouds. Interstellar dust comprises various elements, ranging from hydrogen to titanium, contrasting with the carbon composition of smoke.
Astrophysicists have long speculated about the ISM, but recent advancements in telescope technology since the 1940s have enhanced our understanding of its size and function. Comprising around one-seventh of the universe’s matter, the ISM plays a crucial role in star formation. However, the changes in the ISM since the universe’s inception remain a mystery.
To delve into the ISM’s history, Stephen Eales and Bradley Ward from Cardiff University analyzed the average density and temperature of cosmic dust over time. These two factors influence how dust particles aggregate, as they serve as the fundamental building blocks for stars. The clumpiness of dust determines the timing, location, and quantity of star formation.
Scientists have observed disruptions in the ISM, prompting smaller fragments to merge, ultimately leading to the condensation and fusion of hydrogen into helium, transforming cold, dark dust clouds into stars. Nonetheless, for stars to form, the clouds must maintain sufficient density and coldness to stay united.
Utilizing two methods, Eales and Ward estimated the temperature and density of interstellar dust across a series of galaxies. They employed light emissions from galaxies in an international study and the Herschel-ATLAS Survey to gauge temperature. Physicists have long established a relation between heat and light, whereby objects emit light above absolute zero, with hotter substances emitting more light. Less light indicates cooler dust, while more light suggests warmer dust.
Eales and Ward discovered that cosmic dust in the ISM has maintained a temperature of 22 Kelvin (-251 degrees Celsius or -420 degrees Fahrenheit) over the past 7 billion years, conducive to star formation. They proposed that this stable temperature might have persisted even further back in time.
Their team also analyzed dust density by studying data from the same sky section, using the Hubble Space Telescope. By determining the galaxies’ sizes and volumes and accounting for distance-induced size differences due to galaxy age, they calculated dust mass. Chemical tables aided in estimating the mass per dust particle, enabling an overall dust mass calculation for each galaxy.
Eales and Ward then calculated dust density by dividing the total dust mass by the galaxy’s volume. They observed an increase in dust density, peaking around 10 billion years ago after a rise starting approximately 14 billion years post-Big Bang. The subsequent decline aligns with star formation rates, indicating a diminishing supply of star-forming material in the universe.
This trend led the researchers to foresee a potential slowdown in star formation, eventually leading to a universe populated solely by pre-existing stars. They recommended measuring optical emissions from more distant dust to enhance the understanding of the universe’s past and future. By expanding the data set, scientists could diminish estimation uncertainty and refine cosmic dust’s historical trajectory.
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Source: sciworthy.com
