A combination of X-ray, optical, and infrared data reveal the central pulsar at the core of the Crab Nebula, including the winds and outflows that the pulsars carry in the surrounding matter. The central bright purplish-white spot is, indeed, the Crab pulsar, which itself spins at about 30 times per second. The material shown here spans about 5 light-years in extent, originating from a star that went supernova about 1,000 years ago, teaching us that the typical speed of the ejecta is around 1,500 km/s. The neutron star originally reached a temperature of ~1 trillion K, but even now, it’s already cooled to “only” about 600,000 K. (Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech)

From the hottest to the coldest places in the Universe

We can’t go back to the Big Bang, nor ahead to the heat death of the Universe. Nevertheless, here are today’s natural temperature extremes.

The visible Universe is full of temperature extremes.

The galaxy Centaurus A is the closest example of an active galaxy to Earth, with its high-energy jets caused by electromagnetic acceleration around the central black hole. The extent of its jets are far smaller than the jets that Chandra has observed around Pictor A, which themselves are much smaller than the jets found in massive galaxy clusters. This picture, alone, illustrates temperatures ranging from ~10 K to as high as several millions of K. (Credit: X-ray: NASA/CXC/CfA/R.Kraft et al Radio: NSF/VLA/Univ. of Hertfordshire/M.Hardcastle et al. Optical: ESO/VLT/ISAAC/M.Rejkuba et al.)

It’s true: the past was hotter and the future will be colder.

A visual history of the expanding Universe includes the hot, dense state known as the Big Bang and the growth and formation of structure subsequently. The full suite of data, including the observations of the light elements and the cosmic microwave background, leaves only the Big Bang as a valid explanation for all we see. As the Universe expands, it also cools, enabling ions, neutral atoms, and eventually molecules, gas clouds, stars, and finally galaxies to form. Early on, the highest temperature conditions of all-time were achieved; in the far future, everything will eventually cool off towards absolute zero. (Credit: NASA/CXC/M. Weiss)

But even today, incredibly hot and cold extremes are ubiquitous.

This illustration of a radio-loud quasar that is embedded within a star-forming galaxy gives a close-up look of how giant radio galaxies are expected to emerge. At the center of an active galaxy with a supermassive black hole, jets are emitted that slam into the larger galactic halo, energizing the gas and plasma and causing radio emissions in the form of jets close by the black hole, and then plumes and/or lobes farther away. Both supermassive and stellar-mass black holes have overwhelming evidence supporting their existence, but supermassive black holes may heat matter to the highest temperatures of all, accelerating particles to even beyond the GZK cutoff set by particle physics. (Credit: ESA/C. Carreau)

The hottest environments exist around natural particle accelerators: supermassive black holes.

The radio features shown here, in orange, highlight the giant radio galaxy Alcyoneus, as well as the central black hole, its jets, and the lobes at either end. This feature is the largest known in the Universe to correspond to a single galaxy, and makes Alcyoneus the largest known galaxy in the Universe at present. Although only radio and infrared features are shown here, it radiates in the high-energy portion of the spectrum as well. (Credit: M.S.S.L. Oei et al., Astronomy & Astrophysics, 2022)

When active, their accelerated particles maximally achieve ~10²⁰ eV energies…