"That switchover could only be seen with the Hubble Space Telescope," Mountain said. "The switch is what convinced everybody that dark energy is real." And that, he added, "is probably what convinced the Nobel committee."

Mountain and Riess both gave credit Tuesday to U.S. Sen. Barbara A. Mikulski of Maryland for her political support for Hubble, and to NASA astronauts who risked their lives to keep it working.

Riess has since written a key argument for using the planned Webb Space Telescope to probe beyond the limits of the Hubble to reveal the beginnings of the universe's expansion.

The Webb is said to be about 75 percent complete, with a 2018 launch date. But a $7 billion cost overrun has caught the attention of Congress, putting its NASA funding in jeopardy.

"I think [Riess's Nobel] will help," Mountain said. The Space Telescope Science Institute is expected to manage the Webb's science program. The Webb already accounts for 140 full-time jobs at the institute, and that's expected to grow to 275 after launch.

The Webb's huge mirror and infrared sensors should allow astronomers to see the very first supernovae and another type of star called Cepheid variables, and use them as mileposts to help calculate the changing expansion rate of the universe as it evolved, as well as its size, Mountain said.

It should also show whether dark energy has changed over time, a key to learning just what it is, and thereby solving what Mountain said has been called "one of the greatest mysteries in the universe."

Among the possible implications of dark energy, Mountain said, are that "we either live in a multivariate universe [just one of many]," or "there's a whole force of nature that we haven't discovered yet."

Riess said the work has been "an incredibly exciting adventure." He hopes, when the Nobel hubbub dies down, to go back to his research. Nobel winners are often shunted into supervisory roles, running departments or institutes. "I'd like to actually keep doing science."

At the Space Telescope Science Institute, the mood Tuesday was celebratory.

Mario Livio, an astrophysicist who has co-authored papers with Riess, said the award underscores the importance of having access to powerful telescopes such as the Hubble.

"I was essentially certain he would receive the Nobel Prize someday," Livio said. "The question was, when will they decide to actually give it to him?"

Marc Postman, an astronomer at the institute, collaborates with Riess on projects.

"Sometimes you meet people and you get a sense they're an extra special talent," he said. "Adam is one of those people."

Students arriving to take physics classes Tuesday said they were inspired by Riess' achievement.

"It makes me feel honored to be at Hopkins," said Rohit Bhattacharya, 18.

"In every class, there are esteemed minds," added Austin Jordan, 18. "There are so many great professors here; it's really cool."

Back home in Stoneleigh, south of Towson, neighbors said they've thrown parties for Riess before, when his discovery has won other prizes. They described him as "very humble," "brilliant" and "very well-rounded."

"Adam is probably the shining star of the neighborhood," said Mary Alice Thomas, whose kids play with Riess' children. "To have a Nobel Prize winner across the street is pretty amazing."

Just a few years earlier, in 2003, another Stoneleigh resident, Peter Agre, received news that he won the Nobel Prize for chemistry. At the time, Agre was a biochemist at Hopkins' School of Medicine.