A nova is a sudden, dramatic brightening of a star that can make it visible in the night sky where nothing seemed to exist before. The word comes from the Latin “stella nova,” meaning “new star,” because ancient astronomers thought they were witnessing the birth of a star rather than an explosion on an existing one. If you searched “what is nova,” you may also be looking for the NOVA food classification system used in nutrition research. This article covers both.
How a Nova Works in Space
A nova happens in a two-star system where a dense, compact remnant called a white dwarf orbits close to a larger companion star. The white dwarf’s intense gravity pulls hydrogen gas from the surface of its neighbor, and that stolen gas accumulates on the white dwarf’s surface over time. When enough hydrogen builds up, the pressure and temperature become extreme enough to trigger a runaway nuclear fusion explosion on the surface.
At peak brightness, a nova typically reaches about 100,000 times the luminosity of the Sun. That’s enough to make a previously invisible star suddenly appear to the naked eye, sometimes for days or weeks. But here’s the key detail: the explosion only burns a thin layer of accumulated hydrogen on the surface. The white dwarf itself survives completely intact, and so does its companion star. Once things calm down, the whole cycle starts over as the white dwarf begins pulling hydrogen again.
Astronomers classify novae by how quickly they fade. Very fast novae dim rapidly, losing brightness within days. Slow novae can take weeks or months to return to their original dimness. There’s a reliable pattern here: the brighter the nova, the faster it fades. Slower novae also tend to form dust shells around themselves as they cool, which can be detected in infrared observations.
Types of Novae
Classical novae are the standard type described above: a single recorded explosion on a white dwarf, though the same system will almost certainly erupt again given enough time. Recurrent novae are systems where multiple eruptions have been observed within a human lifetime, sometimes decades apart. The same physics applies, but these systems accumulate fuel faster.
Dwarf novae are a different phenomenon entirely. Rather than a thermonuclear explosion on the white dwarf’s surface, these smaller brightenings come from instabilities in the disk of gas spiraling toward the white dwarf. They’re far less luminous than classical novae and repeat on much shorter timescales, sometimes every few weeks. Despite the name difference, the spectra of old classical novae and dwarf novae look almost indistinguishable to astronomers studying them after the fact.
Nova vs. Supernova
The names sound similar, but the scale is wildly different. A nova reaches about 100,000 times the Sun’s brightness. A supernova reaches billions of times the Sun’s brightness.
The more important distinction is survival. In a nova, the white dwarf lives to erupt again. In a supernova, the star is destroyed. There are two main ways supernovae happen. In one type, a white dwarf accumulates so much mass that it crosses a critical threshold and detonates completely, blowing itself apart with debris racing outward at up to 6% of the speed of light. In the other type, a massive star’s core collapses under its own gravity, and the resulting shockwave tears the outer layers into space. Either way, the original star is gone.
Think of a nova as a surface flash and a supernova as a total detonation. Only a tiny fraction of the white dwarf’s mass is involved in a nova. A supernova consumes the whole thing.
The NOVA Food Classification System
In nutrition science, NOVA (not an acronym, just styled in capitals) is a system that classifies foods by how much industrial processing they’ve undergone. Developed by researchers in Brazil, it sorts every food into one of four groups and has become central to the global conversation about ultra-processed foods and health.
The Pan American Health Organization (PAHO) recommends the NOVA system, and countries including Brazil, Ecuador, Peru, and Uruguay have incorporated it into their national dietary guidelines.
The Four NOVA Groups
- Group 1: Unprocessed or minimally processed foods. These are whole foods or foods altered only by removal of inedible parts, drying, freezing, pasteurizing, or fermenting. Think fresh fruit, eggs, plain milk, dried beans, and fresh meat.
- Group 2: Processed culinary ingredients. Substances extracted from Group 1 foods and used in cooking, such as oils, butter, sugar, salt, and flour. You wouldn’t eat these on their own, but you use them to prepare meals.
- Group 3: Processed foods. Group 1 foods modified by adding Group 2 ingredients in simple ways: canned vegetables with salt, cheese, freshly baked bread, cured meats. These typically have two or three ingredients and are recognizable versions of the original food.
- Group 4: Ultra-processed foods. Industrial formulations made mostly or entirely from substances derived from foods, plus additives rarely used in home cooking. The hallmarks are ingredients like emulsifiers, sweeteners, preservatives, and artificial colors. Soft drinks, packaged snacks, instant noodles, reconstituted meat products, and most mass-produced packaged baked goods fall here.
Why the NOVA System Matters for Health
A large meta-analysis of prospective studies, published in Advances in Nutrition, found that people who ate the most ultra-processed foods (Group 4) had consistently higher risks of several chronic conditions compared to those who ate the least. The numbers are striking: a 37% higher risk of developing type 2 diabetes, a 32% higher risk of hypertension, and a 32% higher risk of obesity. The links to blood fat problems were even steeper, with a 47% increased risk of high triglycerides and a 43% increased risk of low “good” cholesterol.
Cardiovascular disease shows a similar pattern. In the long-running Framingham Offspring Study, each additional daily serving of ultra-processed food was associated with a 7% increase in cardiovascular disease risk over 18 years of follow-up. A large French cohort study found a 12% increased risk of cardiovascular disease with higher ultra-processed food consumption.
These are observational findings, meaning they show a strong pattern but can’t prove that ultra-processed foods directly cause these conditions. Still, the consistency across multiple large studies and different populations is what has driven public health agencies to pay attention. The practical takeaway is straightforward: meals built primarily from Group 1 foods, prepared with Group 2 ingredients, are consistently linked to better long-term health outcomes than diets heavy in Group 4 products.
Spotting Ultra-Processed Foods
The simplest test is the ingredient list. If a product contains substances you wouldn’t find in a home kitchen, such as high-fructose corn syrup, hydrogenated oils, protein isolates, emulsifiers, thickeners, or artificial flavors, it’s almost certainly Group 4. The more ingredients a packaged food has, and the less recognizable those ingredients are, the more likely it fits the ultra-processed category.
This doesn’t mean all processing is harmful. Pasteurized milk, frozen vegetables, and canned beans are all processed to some degree but remain in Group 1 or Group 3. The NOVA system draws its sharpest line at industrial additives and formulations designed to be hyper-palatable, convenient, and shelf-stable, often at the cost of nutritional quality.