Before agar, microbiologists had experimented with other foodstuffs as microbial media. They turned to substances rich in the starches, proteins, sugars, fats, and minerals that organisms need for growth, testing with broths, bread, potatoes, polenta, egg whites, coagulated blood serums, and gelatine. However, none worked particularly well: all were easily broken down by heat and microbial enzymes, and their surface, once colonized, became mushy and unsuitable for isolating microbes.
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It's not yet clear why researchers decided to point Webb in its direction, but little is known about the nebula, including the mass of the star creating it. That matters because a more massive star could eventually explode as a supernova, while a smaller, sun-like star would keep shrugging off layers of material until only a dense core remains and cools over time.