What is the biggest thing in the universe?

The biggest things in the universe, step by step

Space gets big very quickly. Each step in this table is many times bigger than the one before. A light-year is the distance light travels in a year, about 9.46 trillion km.

Here is the whole range, from the smallest length physics can describe to the observable universe, in metres. Each step of 1 in the power of ten means 10 times bigger.

From the smallest length physics can describe to the edge of the observable universe is a factor of about 10⁶². Practise writing numbers like these with our Scientific Notation Calculator, then try this question on powers of ten:

The largest structures: superclusters and superstructures

Galaxies aren't scattered evenly. They gather into groups and clusters, and clusters gather into superclusters, strung along threads and sheets with huge empty voids between them, a pattern called the cosmic web.

• Laniakea is the supercluster our Milky Way belongs to. A 2014 study in Nature mapped it as containing the mass of 10¹⁷ Suns and about 100,000 large galaxies, across roughly 500 million light-years. Its name comes from the Hawaiian words for "heaven" and "spacious".
• Quipu is a chain of galaxy clusters announced in February 2025. The Max Planck Institute for Extraterrestrial Physics called it the largest superstructure ever reliably characterised, about 1.4 billion light-years long, made mainly of dark matter. It is named after the Inca knotted cord records it resembles.

Even Quipu is only about 1.5% of the width of the observable universe. Other, larger structures have been proposed from patterns in distant quasars and gamma ray bursts, but astronomers still debate whether they are real structures or chance patterns, so they don't hold a firm record.

What is the biggest star in the universe?

The biggest stars are red supergiants: old, massive stars that have swollen enormously near the end of their lives. In November 2024, ESO released the first close-up picture of a star in another galaxy, WOH G64 in the Large Magellanic Cloud, over 160,000 light-years away. It is roughly 2,000 times the size of the Sun. Placed where the Sun is, a star that size would stretch far beyond Earth's orbit.

Which star is the very biggest is hard to say. These stars have no sharp surface, they are often wrapped in dust, and their distances are uncertain, so size estimates change as measurements improve. WOH G64 is one of a handful of red supergiants competing for the title.

What is the biggest planet in the universe?

In our Solar System it is Jupiter. NASA says it is 11 times wider than Earth and has more than twice the material of all the other bodies in the Solar System combined. Beyond the Solar System, astronomers have found gas giants that are wider than Jupiter, puffed up by heat from stars they orbit closely. But a planet can't get much heavier than Jupiter before it becomes something else: a heavier object starts nuclear reactions and counts as a brown dwarf, a "failed star".

What is the smallest thing in the universe?

Atoms are made of protons, neutrons and electrons, and protons and neutrons are made of quarks. A proton's radius is about 8.4 × 10⁻¹⁶ m, according to NIST. Electrons and quarks are smaller still: as far as any experiment can tell, they have no size at all and behave like points. The smallest length physics can make sense of is the Planck length, about 1.6 × 10⁻³⁵ m (NIST, 2022 values). Near that scale, gravity and quantum physics would both matter at once, and today's theories stop working.

The Smallest Thing course zooms down this ladder step by step. Try it: this question gives you statements about the very small and asks which are true.

What is the hottest thing in the universe?

• The Sun: its surface is about 5,500 °C, its corona reaches about 2 million °C and its core about 15 million °C, according to NASA.
• Human made records: particle colliders smash heavy atomic nuclei together to make a quark gluon plasma, the state of matter that filled the universe just after the Big Bang. Brookhaven's RHIC collider measured its plasma at around 4 trillion °C, more than 250,000 times hotter than the Sun's core. CERN's ALICE experiment reported in 2012 that its collisions were hotter still, believed to be over 5 trillion kelvin.
• The early universe: the hottest thing of all was the universe itself in the first instants after the Big Bang, hotter than any star or collider since.

Our guide to the Big Bang explains how the universe cooled from that state, and the guide what is the universe? covers whether it is infinite.

Common misconceptions

• "The biggest star is the heaviest star." The widest stars are swollen supergiants; the most massive stars are usually smaller and much hotter.
• "The universe is 13.8 billion light-years across." That is its age in years. The observable part is about 92 billion light-years across.
• "Atoms are the smallest things." They are made of smaller particles, and those may have no size at all.
• "Records are fixed." New surveys keep finding bigger structures and refining star sizes, so treat these as the best current figures.

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